The kanji 洞 primarily means "cave," "hole," or "hollow." It refers to a space that is empty or recessed, often in the earth or a similar solid object. The character evokes a sense of depth and enclosure. It can also figuratively describe something empty or lacking substance.

・On-yomi (音読み): ドウ (dō) ・Kun-yomi (訓読み): ほら (hora)

⚫︎洞窟 Translation: cave ⚫︎空洞 Translation: cavity; hollow ⚫︎山洞 Translation: mountain cave

The kanji 洞 is a phono-semantic compound (形声文字, けいせいいもじ). The left side is a water radical (氵) that suggests a connection with water or liquid, and the right side is "同" (dō) which suggests the sound and possibly the idea of something being the same. Initially, the original form might have been connected with a river or some water cave. Thus, the idea of the "cave" or "hole" is suggested.