In favour of a bit of comfort (3)
I believe the answer is:
for
'in favour of' is the definition.
(being for a particular cause)
'a bit of comfort' is the wordplay.
'a bit of' says the answer is hidden in the clue.
'FOR' is hidden within 'comfort'.
(Other definitions for for that I've seen before include "Pro" , "Favouring" , "Approving" , "In support of" , "See 24" .)