Assumed I put a vet off (8)
I believe the answer is:
putative
'assumed' is the definition.
(thesaurus)
'i put a vet off' is the wordplay.
'off' indicates an anagram.
'i'+'put'+'a'+'vet'='iputavet'
'iputavet' with letters rearranged gives 'PUTATIVE'.
(Other definitions for putative that I've seen before include "Supposed - tie up vat (anag)" , "Supposed or thought to be" , "Supposed, generally considered such" , "Generally considered or reputed to be" , "Supposed or reputed" .)