na-adjective, noun
inarticulate; clumsy with words; poor at speaking
Describes someone who has difficulty expressing themselves verbally, often contrasted with 口上手. The cross-reference 口下手 is a more common synonym.
See also: 口下手
彼は口不調法で、自分の気持ちをうまく伝えられない。
He is inarticulate and can't convey his feelings well.
Even someone who is poor at speaking can sometimes express themselves well in writing.