Oddball (O, not Y) (6)

I believe the answer is:

weirdo

(Other definitions for weirdo that I've seen before include "Informally, an eccentric or very strange person" , "Derogatory term for an eccentric" , "An eccentric (sl.)" , "Slang for odd or eccentric person" , "Unpleasantly strange or eccentric person" .)

I've seen this clue in The Times.

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