Waste time on party ship (4)
I believe the answer is:
doss
'waste time' is the definition.
(informal term meaning to idle)
'on party ship' is the wordplay.
'on' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'ship' becomes 'ss'.
'do' next to 'ss' is 'DOSS'.
(Other definitions for doss that I've seen before include "Sleep in a makeshift bed" , "Sleep - sleeping place" , "going off to sleep" , "Sleep in rough or improvised accommodation" , "Sleep like a tramp" .)