头 is the simplified form of traditional 頭, a pictophonetic compound. In the full form 頭, the element 页 (yè, a stylized human head) carries the meaning, and 豆 (dòu) supplies the sound. The 页 component is the same head that appears in 颜 yán (face), 颈 jǐng (neck), and 顶 dǐng (crown), so the traditional glyph wears its meaning openly: a head, marked by the 页 head-element, pronounced like 豆.

The simplified 头 throws away the phonetic and the head-element alike, replacing them with a compact cursive shape that the dictionaries file under the radical 大 (dà, big). It no longer pictures anything; it is a shorthand glyph standing in for the older 頭. The two are one word, one reading: write 头 on the mainland and in simplified texts, 頭 in traditional Taiwan, Hong Kong, and classical printing.

From the body part, the meaning radiates outward in four directions:

1. The head (body part). The top of the body: 头发 tóufa (hair), 点头 diǎntóu (to nod), 抬头 táitóu (to raise the head).
2. Top, tip, end, beginning. The head of a thing, either extremity of it: 山头 shāntóu (hilltop), 街头 jiētóu (street corner), 开头 kāitóu (the start), 尽头 jìntóu (the very end).
3. Chief, leader, the one at the head. 头目 tóumù (ringleader), 领头 lǐngtóu (to take the lead).
4. The toneless noun-suffix (tou). Bleached of meaning, it just marks a concrete noun: 石头 shítou (stone), 木头 mùtou (wood), 馒头 mántou (steamed bun). It also serves as a measure word for livestock: 一头牛 yī tóu niú (one cow).

The thread is the head as the top, leading end of anything: of a body, of a hill, of a street, of a group, even the leading edge of a noun.

Once 头 means "the head of a thing," it can name either extremity of it. The head of a street is the corner where it starts (街头 jiētóu); the head of a hill is its summit (山头 shāntóu). Stretched along a line, 头 marks the leading edge: 开头 kāitóu is the very start, the place where a thing first pokes its head out, while 尽头 jìntóu is the point where it runs out, the far end of the road.

This is why 头 sits naturally with directions and edges. 前头 qiántou (in front), 后头 hòutou (behind), 上头 shàngtou (on top), and 里头 lǐtou (inside) all use the toneless suffix to turn a bare position word into a place-noun. In each, 头 supplies the sense of "the edge, the end-point in that direction."

Like 子 (zi) and 儿 (r), 头 does double duty as one of Mandarin's empty noun-suffixes. Drained of its full second tone, toneless 头 (tou) attaches to a one-syllable root and turns it into a stable, two-syllable noun: 石头 shítou (stone), 木头 mùtou (wood), 骨头 gútou (bone), 舌头 shétou (tongue), 馒头 mántou (steamed bun). The root often cannot stand alone, and 头 fills the second slot to mark "this is a thing."

Listen for the tone, just as with 子. A full rising tóu is the meaningful head: 抬头 táitóu, 开头 kāitóu, 山头 shāntóu. A neutral tou is the bare suffix: 石头 shítou, 木头 mùtou. The reading is your clue to which 头 you are meeting.

Separately, 头 (tóu, full tone) serves as the measure word for large livestock: 一头牛 yī tóu niú (a cow), 三头猪 sān tóu zhū (three pigs), 一头大象 yī tóu dàxiàng (an elephant). The image is counting beasts by their heads, much as English once counted cattle by the head.

Start at the top of the body: the head, 头. Now let "the head of a thing" travel. Put it on a hill and you reach the summit (山头). Put it on a street and you reach the corner (街头). Lay it along a line and it becomes the leading end, the beginning (开头), with the far end, the place it runs out, as its mirror (尽头). Put it over a group and it becomes the chief, the one at the head (头目).

Then watch it empty out entirely. Toneless, 头 (tou) drops all of this and becomes the bare tag that makes a thing a thing: 石头 stone, 木头 wood, 馒头 bun. The tone is your guide back, as with 子: a rising tóu is a meaningful head or end, a neutral tou is only the suffix. And when you count cattle, hear the full tóu return: 一头牛, one beast, counted by its head.