않다
anta · TOPIK 2
to not do (negative auxiliary)
않다 = 아니 (not) + 하다 (do), squeezed into one syllable
Etymology: 않다 is a contraction of 아니하다, literally not + do. The ㅎ left over from 하다 hides in the final consonant, which is why 않 + 다 is pronounced anta, with a puffed t. Attach it after a verb stem + 지: 가지 않다 = to not go.