I. ˈone-off 1 BrE AmE adjective [only before noun] British English
happening or done only once, not as part of a regular series SYN one-shot American English :
It’s yours for a one-off payment of only £200.
II. ˌone-ˈoff 2 BrE AmE noun [countable] British English
1 . something that is done or made only once:
The deal was a one-off.
2 . informal someone who is completely different from anyone else