空 (kōng): empty; hollow

Meanings

1 empty; hollow
2 air; sky
3 in vain; for nothing

Characters

Cave radical 穴 over 工 — a hollowed-out cavity. Read kōng for the abstract 'empty/sky/in vain' senses, kòng for the concrete 'vacant slot/free time' senses.

Examples

这个房间是空的。

Zhège fángjiān shì kōng de.

This room is empty.

天空很蓝。

Tiānkōng hěn lán.

The sky is very blue.

别空想，要行动。

Bié kōngxiǎng, yào xíngdòng.

Don't daydream — take action.

Tips

grammar

Two readings. 空 (1st tone) covers the abstract senses — empty, hollow, sky, in vain — and dominates the compound list: 天空, 空气, 太空, 空军, 航空, 空想. 空 (4th tone) is the concrete 'vacant slot / free time' sense: 有空, 空儿, 空缺, 空白, 钻空子.

memory

Tone follows the abstraction. Empty as a state of the world (sky, air, in vain) → 1st tone kōng. Empty as an opening you can step into (a slot in the schedule, a vacancy, a blank on the form) → 4th tone kòng. If you can point at it and fill it, it's 空.

Components

radical

穴 xué

cave; hole

Cave radical on top — pictures a dwelling-pit roofed by 宀 with two leg-strokes for the opening. It marks 空 as a member of the cave/hollow family alongside 穿 (pierce through), 窗 (window) and 究 (probe deeply). The hollow inside the cave gave 空 its 'empty' meaning.

phonetic

工 gōng

work; tool

工 sits under the cave to give the sound, which then nasalised into kōng. The same 工-phonetic threads through 红, 江, 项 and 攻 — a useful little family. Here it is purely sonic; the meaning of 'empty' all comes from the 穴 above.