Opposite of 'odd' (4)
I believe the answer is:
even
'opposite of odd' is the definition.
('even' is the opposite to 'odd')
This is all the clue.
(Other definitions for even that I've seen before include "When darkness starts to fall" , "Crisp and ---, how King Wenceslas found the snow" , "exact" , "of consistent quality" , "Flat, regular" .)