I. ˈone-off1 adjective [only before noun] British English happening or done only once, not as part of a regular series
Synonym : one-shot American English:
It’s yours for a one-off payment of only £200. [TahlilGaran] Dictionary of Contemporary English ▲
II. ˌone-ˈoff2 noun [countable] British English1. something that is done or made only once:
The deal was a one-off.2. informal someone who is completely different from anyone else
[TahlilGaran] Dictionary of Contemporary English ▲