洞 (dòng) · cave; cavern

Meanings

1 cave; cavern
2 hole; opening
3 zero (unambiguous spoken form when reciting digits)

Characters

洞

dòng

cave; hole

Examples

HSK 3

山上有一个大洞。

Shānshàng yǒu yígè dàdòng.

There's a big cave on the mountain.

HSK 3

电话号码是一三洞。

Diànhuà hàomǎ shì yāo sān dòng.

The phone number is one-three-zero.

HSK 4

袜子破了一个洞。

Wàzi pò le yī ge dòng.

There's a hole in the sock.

Tips

usage

Reading digits aloud, 洞 replaces 零 for 'zero' to avoid mishearing - common in military, aviation, and phone-number recitation. Pair with 幺 (for 一, to avoid confusion with 七): 幺三洞 = 1-3-0.

memory

氵 (water) + 同 (same; through) - a water-cut passage 'going through'. The phonetic 同 shifted only in tone to dòng (2nd → 4th); the same phonetic appears in 桐 (paulownia), 铜 (copper), 筒 (tube).

Components

radical

氵 shuǐ

water (radical)

Three-drop water radical on the left - the side-stacking form of 水. Original sense of 洞 was a water-cut hole: a cave hollowed out by a stream, a sinkhole, an underground passage. From those literal cave-mouths the meaning broadened to any opening or hole, including figurative ones (洞察, to see clearly through).

phonetic

同 tóng

same; together

Right 同 supplies the sound - tóng shifted only in tone to dòng (2nd → 4th). 同 is itself a hollow shape (a frame around 一 + 口, suggesting a pipe or tube), giving a faint semantic echo of an empty channel. Family with same phonetic: 桐 (paulownia), 铜 (copper), 筒 (tube).