Peck, smack (4)
I believe the answer is:
kiss
I believe this clue is a double definition.
'peck' is the first definition.
(I know that peck can be written as kiss)
'smack' is the second definition.
(smack can informally mean a kiss)
(Other definitions for kiss that I've seen before include "Act of love" , "Expression of love" , "Peck (on cheek or lips?)" , "Peck, smacker, X" , "Caress with lips" .)