In September are rabbits less common? (5)
I believe the answer is:
rarer
'less common?' is the definition.
('rare' can be the opposite of 'common' so perhaps 'rarer' is reasonable for 'less common')
'in september are rabbits' is the wordplay.
'in' says the answer is hidden in the clue.
'RARER' is hidden within 'september are rabbits'.
(Other definitions for rarer that I've seen before include "Thinner" , "(Of meat) less cooked" , "less easy to find" , "even less common" , "Less frequent" .)