Caution - dubious gift horse! (9)
I believe the answer is:
'caution' is the definition.
(I've seen this before)
'dubious gift horse' is the wordplay.
'dubious' indicates an anagram.
'gifthorse' with letters rearranged gives 'FORESIGHT'.
(Other definitions for foresight that I've seen before include "Ability to anticipate" , "Prudence" , "Anticipation" , "Clairvoyance" , "Vision" .)