Counter bachelor’s gibe (4)
I believe the answer is:
barb
'gibe' is the definition.
(both can mean an unkind comment)
'counter bachelor's' is the wordplay.
'counter' becomes 'bar' (bar is a kind of counter).
'bachelor' becomes 'B' (abbreviation e.g. BA=Bachelor of Arts).
'bar'+'b'='BARB'
(Other definitions for barb that I've seen before include "Sharp projection" , "Kind of thorn or wounding remark" , "Small prong on larger point" , "Aggressive remark directed at a person" , "Jag on a hook" .)