na-adjective, noun
inarticulate; poor at speaking; clumsy with words
Describes someone who has difficulty expressing themselves verbally, often contrasted with 話し上手. Can be used as a noun or na-adjective.
彼は口下手だから、自分の気持ちをうまく伝えられない。
He is inarticulate, so he can't convey his feelings well.
口下手な人でも、練習すれば話せるようになる。
Even people who are poor at speaking can learn to talk with practice.
Compound of 口 (mouth, speech) and 下手 (unskillful). The reading くちべた is a standard kun'yomi combination.