Loud kiss (9)
'loud kiss' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for smack that I've seen before include "Sharp slap" , "Loud kiss" , "Hit with an open hand" , "Heroin (sl.)" , "Hit - fishing vessel" .)
(Another definition for smackeroo that I've seen is " dollar".)
(Other definitions for smacker that I've seen before include "Loud kiss - GBP1" , "Loud kiss -- PS1" , "pound" , "someone taking part in strike?" .)