What does “이가 흔들리다” mean in Korean?

A wobbly baby tooth in Korean isn’t “loose” — it shakes. You say 이가 흔들려요, literally “the tooth wobbles,” using 흔들리다, the very same verb for a swaying tree or a building that shakes in the wind. It’s the passive of 흔들다 (“to shake something”), so when a child actively wiggles the tooth themselves, that flips back to 흔들다: 이를 흔들어요.

The pair is one of Korean’s clearest passive contrasts: 흔들다 = “to shake (something),” 흔들리다 = “to be shaken / to wobble” — the -리- syllable does the work, the same -이/-히/-리/-기 family that turns 보다→보이다 and 듣다→들리다. Useful body vocab rides along too: 윗니 (upper tooth) and 아랫니 (lower tooth), both built on 이/니 (tooth), so 윗니가 흔들려요 is “my top tooth is loose.”