Opposite of even (3)
I believe the answer is:
odd
'opposite of even' is the definition.
('odd' is the opposite to 'even')
This is all the clue.
(Other definitions for odd that I've seen before include "Peculiar or unpaired" , "Not even? That's peculiar" , "Matchless" , "Peculiar in uneven way" , "Not even - curious" .)