Only a bit of baloney (4)
I believe the answer is:
lone
'only' is the definition.
('lone' can be a synonym of 'only')
'a bit of baloney' is the wordplay.
'a bit of' says the answer is hidden in the clue (I've seen 'a bit' mean this (the answer is formed by a bit of the clue)).
'LONE' is hidden within 'baloney'.
(Other definitions for lone that I've seen before include "Single and isolated" , "Unaccompanied" , "The ... Ranger, fictional masked cowboy" , "He likes to operate by himself" , "Solitary, sounds like advance" .)