Insect returning, say - stupid (5)
I believe the answer is:
midge
'insect' is the definition.
(midge is a kind of insect)
'returning say stupid' is the wordplay.
'returning' says the letters should be written in reverse.
'say' becomes 'eg' (both can mean 'for example').
'stupid' becomes 'dim' (similar in meaning).
'eg'+'dim'='egdim'
'egdim' back-to-front is 'MIDGE'.
(Other definitions for midge that I've seen before include "Dipterous insect, in swarms by water" , "Tiny swarming fly" , "Small flying insect" , "Minute mosquito-like fly" , "Gnat" .)