Prolong a short trip abroad (4,3)
I believe the answer is:
spin out
'prolong' is the definition.
(spinning out is a kind of prolonging)
'a short trip abroad' is the wordplay.
'a short trip' becomes 'spin' (go for a spin).
'abroad' becomes 'out' (I've seen this before).
'spin'+'out'='SPIN OUT'
(Other definitions for spin out that I've seen before include "keep going longer" , "Message for fast bowlers only" , "jaunt in car" , "Prolong" .)