Subsequent difficulty about kiss (4)
I believe the answer is:
next
'subsequent' is the definition.
(I've seen this before)
'difficulty about kiss' is the wordplay.
'difficulty' becomes 'net' (net can mean a difficulty).
'about' means one lot of letters goes inside another.
'kiss' becomes 'x' (X can represent a kiss).
'net' placed around 'x' is 'NEXT'.
(Other definitions for next that I've seen before include "Succeeding" , "Neighbour lives in the house . . . . door" , "Immediately afterwards" , "The one following or adjacent" , "Coming nearest in time or sequence" .)