unsuitable; unfit; not suited
Used for people, things, or situations that are not well matched to a purpose, role, or condition. Often appears in the pattern 〜に不向きだ or 〜には不向きだ.
This job is not suited for him.
This computer isn't suited for gaming.
This material is unsuitable for outdoor use.
I think customer service work doesn't suit him.
適する is the formal verb meaning 'to be suited to', whereas 不向き is the casual na-adjective used to say something is unsuited.
向き means 'suitable' or 'well-matched', while 不向き is its direct negation meaning 'unsuitable'.
不向き (an adjectival noun) means 'unsuited', the opposite of 向く used in the sense of being suited to a role or task.
不向き means 'unsuited' for a purpose, the opposite of 持ってこい, which means 'perfectly suited' for a purpose.
Formed from the prefix 不 (fu-, 'not') and 向き (muki, 'suitability, direction'), literally 'not suitable'.