Mosquito given smack on the counter (4)
I believe the answer is:
gnat
'mosquito' is the definition.
(gnat is a kind of mosquito)
'smack on the counter' is the wordplay.
'smack' becomes 'tang' (synonyms).
'on the counter' says the letters should be written in reverse (counter can mean in the opposite direction).
'tang' back-to-front is 'GNAT'.
'given' acts as a link.
(Other definitions for gnat that I've seen before include "Tiny biter" , "Any of various small biting flies" , "insect's" , "Small biter" , "Woodland area" .)