- not mentionable; inappropriate, unfit, or improper for mention, as in polite conversation; unspeakable.
- something that is not to be mentioned: That subject was classed among the unmentionables.
- (formerly) trousers or breeches.
- unsuitable or forbidden as a topic of conversation
- (as noun)the unmentionable
adj.1837, from un- (1) “not” + mentionable. Unmentionables “trousers” is attested from 1823; meaning “underwear” is recorded from 1910.