Unique person (3-3)
I believe the answer is:
one-off
'unique person' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for one-off that I've seen before include "Happening only once" , "Unique specimen" , "Item made once only" , "Unique person or occurrence" , "Made or done as a single thing, not repeated" .)