Join a girl and kiss (5)
I believe the answer is:
annex
'join' is the definition.
(I've seen this before)
'a girl and kiss' is the wordplay.
'a girl' becomes 'anne' (girl's name).
'and' says to put letters next to each other.
'kiss' becomes 'x' (X can represent a kiss).
'anne'+'x'='ANNEX'
(Other definitions for annex that I've seen before include "Append" , "Seize" , "Add by conquest or occupation" , "Attach(ment)" , "Extension to a main building" .)