Top primate gets kiss (4)
I believe the answer is:
apex
'top' is the definition.
(apex is a top or peak)
'primate gets kiss' is the wordplay.
'primate' becomes 'ape' (ape is a kind of primate).
'gets' says to put letters next to each other.
'kiss' becomes 'x' (X can represent a kiss).
'ape'+'x'='APEX'
(Other definitions for apex that I've seen before include "Top, peak" , "Apogee, summit" , "crown" , "climax" , "Uppermost tip" .)