Motivation for vet in nice resort (9)
I believe the answer is:
incentive
'motivation' is the definition.
(I know that incentive is a type of rational motive)
'vet in nice resort' is the wordplay.
'resort' is an anagram indicator (re-sort the letters).
'vet'+'in'+'nice'='vetinnice'
'vetinnice' with letters rearranged gives 'INCENTIVE'.
'for' is the link.
(Other definitions for incentive that I've seen before include "A motivation" , "Motivating payment" , "encouragement" , "Stimulus" , "Something that motivates" .)