A short trip is dull (4)
I believe the answer is:
arid
'dull' is the definition.
(thesaurus)
'a short trip' is the wordplay.
'short' means to remove the last letter.
'trip' becomes 'ride' (I've seen this before).
'ride' with its last letter taken off is 'rid'.
'a'+'rid'='ARID'
'is' acts as a link.
(Other definitions for arid that I've seen before include "Lacking sufficient rainfall" , "Dry and sere" , "Parched and barren" , "Dry and withered" , "Tedious; short of rain" .)