Not used to an event or thing, not accustomed.

simple past tense and past participle of unaccustom

One who does not believe, particularly in a deity (used by believers to describe people who do not believe in the same deity or deities as themselves).

An absence (or rejection) of belief, especially religious belief

(manner) In a manner that one does not or cannot believe. / (degree) To an extent not to be believed. / (evaluative) Contrary to expectations, amazingly.

(UK) A private road, where the local borough council is not responsible for the road's maintenance.

That cannot be beaten, defeated or overcome

Someone or something that can't be beaten

That does not believe; incredulous, skeptical.

Not asked about.