快 kuài

快

kuài

fast · quick · happy · pleased

部首 bùshǒu · 忄heart 7 笔画 bǐhuà strokes HSK 2 tone 4 · kuài

笔顺 bǐshùn · Stroke order

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字源 zìyuán Etymology & Structure

字源洞见 zìyuán dòngjiàn · Etymological Insight

快 kuài = 忄xīn (heart, the upright three-stroke radical form) + 夬 guài (a notch; a decision made with a cut). The phonetic component 夬 depicts a hand pressing down on an object until it snaps: a clean, decisive break. Place that act inside the heart and the result is a heart that has broken free of hesitation — moving forward without drag. That is 快 in its oldest sense: unobstructed, released, cutting through.

The bronze inscription form already shows the heart-and-notch composition clearly. The Shuōwén Jiězì (121 CE) defines 快 as 喜也, "pleasure," but the motion sense was equally present in early texts. Speed and happiness are not two borrowed meanings grafted onto one phonetic shell; they are the same image seen from two angles. A fast river is 快 because the water runs without resistance. A happy person is 快 because the heart runs without resistance.

The phonetic 夬 guài survives in a small family: 决 jué (to decide; to cut through), 缺 quē (a gap; something missing), and 诀 jué (a knack; a parting). All carry the sense of a clean break or decisive separation. 快 sits in that family as the emotional dimension: the feeling of having cut loose.

In Japanese, 快 (read kai in compounds or koころよい kokorogashii natively) stays close to the pleasant/comfortable reading: 快適 kaitekina (comfortable), 快感 kaikan (pleasurable sensation), 爽快 sōkai (refreshing). Korean uses 쾌 kwaé in the same borrowed compounds.

速度 sùdù Speed & Urgency

构词规律 gòucí guīlǜ · Speed Pattern 快 + noun → 快速 fast-speed · 快车 express-train · 快递 express-delivery
verb + 快 → 加快 add-fast (accelerate) · 飞快 fly-fast (lightning speed)
快 + verb → 快点 quick-a-bit (hurry up) · 赶快 catch-quick (do something at once)

快速 kuàisù fast; rapid; at high speed

Adj 形容词 xíngróngcí

快 kuài (fast) + 速 sù (speed; velocity). The compound reinforces both components, producing the most neutral, all-purpose word for fast in formal or written Chinese. Works as an adjective before nouns or as an adverb before verbs.

火车快速通过隧道。

Huǒchē kuàisù tōngguò suìdào.

The train passed through the tunnel at high speed.

他快速回复了我的消息。

Tā kuàisù huífù le wǒ de xiāoxi.

He replied to my message quickly.

这是一个快速发展的城市。

Zhè shì yīgè kuàisù fāzhǎn de chéngshì.

This is a rapidly developing city.

辨析 biànxī · 快 vs 快速单音节 kuài works as a simple predicate adjective (火车很快) or in compounds. 快速 is preferred as a pre-verb adverb in written Chinese or when modifying a noun attributively (快速发展). In spoken Mandarin, 很快 largely fills both slots.

加快 jiākuài to accelerate; to speed up

V 动词 dòngcí

加 jiā (to add; to increase) + 快 kuài (fast). Adding more speed to something already in motion. Common in official and news language for policy goals, construction schedules, and economic development; equally at home in everyday speech.

我们需要加快进度。

Wǒmen xūyào jiākuài jìndù.

We need to speed up the progress.

他的脚步明显加快了。

Tā de jiǎobù míngxiǎn jiākuài le.

His footsteps noticeably picked up.

赶快 gǎnkuài hurry up; do it right now

V 动词 dòngcí

赶 gǎn (to catch up; to rush) + 快 kuài (fast). Used when something needs to happen without delay. Always an adverb modifying a following verb; it conveys urgency rather than habitual speed, with an implicit time pressure in the context.

赶快走，要迟到了！

Gǎnkuài zǒu, yào chídào le!

Get moving, we're going to be late!

你赶快去医院吧。

Nǐ gǎnkuài qù yīyuàn ba.

You should get to the hospital right away.

辨析 biànxī · 赶快 vs 快点赶快 gǎnkuài stresses urgency from external pressure (catch the bus, the situation is critical). 快点 kuài diǎn is the everyday informal command — the thing you say to a child dawdling over breakfast, less dramatic in register.

快点 kuài diǎn be quick; a bit faster; hurry

V 动词 dòngcí

快 kuài (fast) + 点 diǎn (a little; somewhat — the softening particle). The most colloquial way to tell someone to speed up. Tonal in its delivery: said gently it is a nudge, said sharply it is impatient.

快点，他们都在等我们呢！

Kuài diǎn, tāmen dōu zài děng wǒmen ne!

Hurry up, they're all waiting for us!

能不能快点儿说完？

Néng bu néng kuài diǎnr shuō wán?

Can you finish saying it a bit faster?

飞快 fēikuài lightning fast; at a flying pace

Adj 形容词 xíngróngcí

飞 fēi (to fly) + 快 kuài (fast). Vivid intensifier: the speed of something that seems to fly. Functions as an adverb modifying a verb or as a predicate adjective. Also used for a blade that is razor-sharp — fast at cutting.

她飞快地跑出了教室。

Tā fēikuài de pǎo chū le jiàoshì.

She bolted out of the classroom.

时间过得飞快。

Shíjiān guò de fēikuài.

Time is passing at a flying pace.

快乐 kuàilè Happiness & Pleasure

辨析洞见 biànxī dòngjiàn · Distinguishing the Happiness Words

快 in the happiness domain does not name a steady state. The heart has cut loose from something — worry, restraint, a long wait — and that release is 快. Compare 高兴 gāoxìng (elevated mood; pleased about something that just happened, reactive and specific) with 快乐 kuàilè (a broader, more durable joy, closer to contentment and happiness as a condition of being). A child wins a prize and is 高兴; a person at peace with their life is 快乐.

The compound 痛快 tòngkuài pushes this further still: 痛 tòng (pain; intensity; wholehearted) + 快 kuài. Something so thoroughly satisfying or so thoroughly frank that it hurts a little. 喝得很痛快 = "drank to the point of real satisfaction." 说得很痛快 = "spoke with total frankness." The word has two distinct registers: frank-to-the-point-of-bluntness, and thoroughly-enjoyable.

快乐 kuàilè happy; joyful; happiness (as a state)

Adj / N 形容词 · 名词

快 kuài (released; unobstructed) + 乐 lè (music; joy; ease). The standard word for happiness in modern Mandarin: functions as an adjective predicate, a pre-noun modifier, and a noun. Appears in greetings and fixed phrases far more than the simple 快 alone.

祝你生日快乐！

Zhù nǐ shēngrì kuàilè!

Happy birthday to you!

她是一个很快乐的人。

Tā shì yīgè hěn kuàilè de rén.

She is a very happy person.

快乐是人生最重要的事情之一。

Kuàilè shì rénshēng zuì zhòngyào de shìqíng zhī yī.

Happiness is one of the most important things in life.

辨析 biànxī · 快乐 vs 高兴快乐 kuàilè = a broader, more enduring state of happiness; used for people, lives, or occasions. 高兴 gāoxìng = pleased, in a good mood, reactive to a specific event. 听到这个消息我很高兴 "I'm pleased to hear that news" — not 快乐, which would sound oddly philosophical in the same slot.

愉快 yúkuài pleasant; cheerful; agreeable

Adj 形容词 xíngróngcí

愉 yú (pleased; at ease; the heart-radical with a sound component suggesting relaxed breathing) + 快 kuài (unobstructed joy). More refined and slightly more formal than 快乐. The word you reach for when describing an experience, a meeting, or an atmosphere as genuinely pleasant.

今天开会的气氛很愉快。

Jīntiān kāihuì de qìfēn hěn yúkuài.

The atmosphere at today's meeting was very pleasant.

我们度过了一段愉快的时光。

Wǒmen dùguò le yīduàn yúkuài de shíguāng.

We spent a pleasant time together.

祝您旅途愉快！

Zhù nín lǚtú yúkuài!

Have a pleasant journey!

快活 kuàihuó carefree; cheerful; lively and at ease

Adj 形容词 xíngróngcí

快 kuài (unobstructed) + 活 huó (alive; living; moving freely). The image is life flowing without constraint. Carries a slightly old-fashioned or literary flavor in modern Mandarin, but remains warm and vivid in fiction and colloquial northern speech. Describes people who seem naturally unburdened.

他整天快活地唱着歌。

Tā zhěng tiān kuàihuó de chàng zhe gē.

He sang cheerfully all day long.

乡下的孩子过得很快活。

Xiāngxia de háizi guò de hěn kuàihuó.

The children in the countryside live with a free and easy cheerfulness.

痛快 tòngkuài frank and direct; thoroughly enjoyable

Adj 形容词 xíngróngcí

痛 tòng (pain; with full intensity) + 快 kuài (free-flowing; pleasurable). Two distinct but related uses. As a personality or speech descriptor: so direct and honest it cuts — blunt, refreshingly frank. As an experience descriptor: so wholly satisfying that nothing was held back. Both senses share the structure of release without restraint.

他说话很痛快，从不拐弯抹角。

Tā shuōhuà hěn tòngkuài, cóng bù guǎiwāncājiǎo.

He speaks frankly and never beats around the bush.

夏天喝一杯冷饮，真痛快！

Xiàtiān hē yī bēi lěngyǐn, zhēn tòngkuài!

A cold drink in summer — that's what I call satisfying!

你就痛快地告诉我答案吧。

Nǐ jiù tòngkuài de gàosù wǒ dá'àn ba.

Just tell me the answer straight out.

文化 wénhuà · Cultural Register 痛快人 tòngkuài rén — "a person who is refreshingly direct" — is a genuine compliment in northern Chinese social culture, where frank dealing is valued. In more face-conscious contexts the same bluntness might be softened or avoided; calling someone 痛快 is reading the room first.

对比 duìbǐ Contrasts — Slow & Unhappy

慢 màn slow; unhurried

Adj 形容词 xíngróngcí

The direct antonym of 快 in the speed domain. 慢 carries the heart radical 忄 as well, perhaps because patience and slowness are also matters of disposition. The pair 快慢 kuài-màn (fast-slow) appears as a compound noun meaning pace or speed level.

这辆车开得太慢了。

Zhè liàng chē kāi de tài màn le.

This car is going too slowly.

慢慢来，不着急。

Màn màn lái, bù zhāojí.

Take your time, there's no rush.

语法 yǔfǎ · Speed Comparison Pattern To compare speeds: A 比 B 快/慢 (+ 一点/得多). 他跑得比我快多了 "He runs much faster than me." The complement of degree uses 得: 她跑得很快 "She runs fast."

不快 bùkuài unhappy; displeased; feeling off

Adj 形容词 xíngróngcí

不 bù (negation) + 快 kuài. The heart is not flowing freely — something is blocking it. Milder and more internal than 不高兴 (visibly in a bad mood); 不快 often describes a quiet dissatisfaction or sense of offense that hasn't been expressed. Literary and somewhat formal; more common in written Chinese than casual speech.

他听了那句话，心里有些不快。

Tā tīng le nà jù huà, xīnli yǒuxiē bùkuài.

He felt a quiet displeasure after hearing those words.

她的神色透露出一丝不快。

Tā de shénsè tòulù chū yī sī bùkuài.

Her expression betrayed a trace of unhappiness.

辨析 biànxī · 不快 vs 不高兴不快 bùkuài is literary, more private — an internal state noted rather than performed. 不高兴 bù gāoxìng is colloquial, describes a visible sulky or displeased manner. A character in a novel might feel 不快; someone visibly sulking at dinner is 不高兴.

成语 chéngyǔ Idioms & Set Phrases

大快人心 dàkuài rénxīn greatly satisfying to the people's hearts — a righteous outcome that pleases everyone Lit: greatly-fast/free-people's-hearts. Used when a wrongdoer receives punishment, a long-overdue verdict is handed down, or a corrupt official is finally removed. The 快 here is squarely in the "heart released from obstruction" sense: justice has cleared away what was blocking everyone. Common in news commentary and public reactions to legal outcomes. Register: formal to neutral written Chinese.

心快口直 xīnkuài kǒuzhí quick heart, straight mouth — frank and direct by nature Lit: heart-fast-mouth-straight. A description of someone whose inner state and outer speech are perfectly aligned — no strategic filtering, no diplomatic softening. Used as a compliment among people who value directness, and occasionally as an excuse after saying something pointed. Paired with the related 心直口快 xīnzhí kǒukuài (same meaning, different character order), which is the more commonly encountered form in modern usage.

快马加鞭 kuài mǎ jiā biān whip a fast horse — press on faster when already moving well Lit: fast-horse-add-whip. The image is of a courier or cavalry rider who is already galloping but spurs the horse harder anyway. Metaphorically: when momentum is good, don't coast. Used to encourage continued effort or accelerated progress, often in workplace or project contexts. Unlike its English near-equivalent "full steam ahead," the Chinese phrase has a slight edge of competitive or urgent drive to it. Common in motivational speeches and planning documents.

记忆法 jìyìfǎ · Master Retention Image

Picture a river running through a gorge. Where the banks narrow and a logjam has built up, the water stalls and darkens. Then the obstruction breaks. The water surges forward, suddenly bright and loud, cutting through the gap at full force. That release is 快 in both its meanings at once: the river moves fast, and the river is glad.

The phonetic component 夬 is the cut, the snap, the moment the log breaks free. The heart radical 忄 tells you this is happening inside a person. Speed is a heart that has stopped holding back. Joy is the same thing.

When you learn 快乐 (happy), 愉快 (pleasant), 痛快 (frank; thoroughly satisfying), 快速 (rapid), and 飞快 (lightning fast), you are watching that same released current moving through different channels. The obstruction that broke was different each time — a long wait, a restrained truth, a slow pace — but the feeling of cutting loose is identical in all of them.