子 zǐ is a pictograph of a swaddled infant. The oracle-bone and bronze forms show a baby with a large round head, arms either raised or wrapped, and the lower body bound in cloth so the legs read as a single stroke. The modern shape preserves this exactly: the top is the head, the long hook is the swaddled body, and the horizontal stroke across the middle is the bundled arms. As a structure the Unihan decomposition reads 子 = ⿻ 了 (liǎo, the hooked body) overlaid with 一 (yī, the cross-stroke of the arms).

From this one image the character spreads into four senses that anchor thousands of words:

1. Child, offspring. The literal meaning. 孩子 háizi (child), 儿子 érzi (son), 子女 zǐnǚ (sons and daughters, i.e. children collectively).
2. Seed, the small generative thing. What a plant or a process produces: 种子 zhǒngzi (seed), 瓜子 guāzǐ (melon seeds), 原子 yuánzǐ (atom, the "original seed").
3. Master, the honorific. Appended to a surname it means "the Master," the respectful title for a teacher or philosopher: 孔子 Kǒngzǐ (Confucius), 孟子 Mèngzǐ (Mencius), 君子 jūnzǐ (the noble person).
4. The empty noun-suffix. Toneless 子 (zi) attaches to a root to mark it as a concrete noun: 桌子 zhuōzi (table), 房子 fángzi (house), 杯子 bēizi (cup). Here 子 has bleached out almost all meaning and survives only as a grammatical tag.

子 is also the first of the twelve Earthly Branches (地支), where it names the hour around midnight and the year of the Rat. The thread running through every sense is smallness and generation: the infant, the seed, the disciple who carries a teacher forward, the bare noun waiting to be made concrete.

The honorific 子 is how classical Chinese names its teachers. Appended to a surname it means "the Master": 孔子 Kǒngzǐ is "Master Kong," whom the West calls Confucius; 孟子 Mèngzǐ is "Master Meng," Mencius; 老子 Lǎozǐ is the "Old Master." The same 子 marks the disciple who carries the teaching onward: 弟子 dìzǐ (disciple), 子弟 zǐdì (the young men of a family or community).

From the title grew an idea of character. 君子 jūnzǐ began as "the ruler's son," the man of the noble class, and Confucius reforged it to mean something earned rather than inherited: the person of cultivated virtue, the moral exemplar. Its foil is 小人 xiǎorén, the petty person. The contrast between 君子 and 小人 runs through the whole Analects, and it remains the everyday Chinese yardstick for whether someone acts honorably.

The busiest job 子 does in modern Chinese is the one where it means almost nothing. Toneless 子 (zi) attaches to a one-syllable root and turns it into a stable, concrete noun: 桌子 zhuōzi (table), 椅子 yǐzi (chair), 房子 fángzi (house), 杯子 bēizi (cup), 鞋子 xiézi (shoes), 帽子 màozi (hat), 本子 běnzi (notebook).

Why does the suffix exist at all? Many of these roots are single syllables that feel incomplete on their own, and Mandarin prefers two-syllable nouns. 子 fills the second slot and signals "this is a thing." It is one of three such noun-suffixes: 子 (zi), 儿 (r, the northern diminutive), and 头 (tou). The choice between them is largely fixed by convention rather than meaning, so the suffix is learned word by word.

Listen for the tone. When 子 is a full word it keeps third tone (zǐ: 君子, 种子, 子女). When it is the bare suffix it goes neutral (zi: 桌子, 孩子, 妻子). The tone is the clearest signal of which 子 you are hearing.

Picture the swaddled infant at the center of 子, then watch it grow outward. The baby is the literal child (孩子, 儿子). Make it tiny and generative and it becomes a seed (种子). Let it grow up under a teacher and it becomes a disciple, and the teacher a 子, a Master (孔子, 君子). Empty it of all meaning and it becomes the bare tag on a noun (桌子, 房子).

The tone is your guide back. A full-tone zǐ is always one of the meaningful 子: child, seed, or Master. A toneless zi is the suffix that means little more than "this is a thing." Hear which one, and you know which 子 you are looking at.