na-adjective, noun
unfit; incompetent; unsuitable
Used to describe a person who is not suitable for a position, role, or task due to lack of ability or character. Often used in formal contexts such as job evaluations or official statements.
彼はその仕事に不適任だと判断された。
He was judged unfit for the job.
不適任な人材を管理職に置く
You should not place an incompetent person in a managerial position.
無能 is a stronger, more direct term for incompetence or inability, often used as a blunt criticism, whereas 不適任 is more formal and situational.
Compound of 不 (not) + 適任 (suitable for a post). 適任 itself is from 適 (suitable) + 任 (duty, responsibility).