Fellow sent diet off (5)
I believe the answer is:
fetid
'off' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'fellow sent diet' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'sent' indicates an anagram (send can mean to excite or stimulate).
'diet' is an anagram of 'etid'.
'f'+'etid'='FETID'
Can you help me to learn more?
(Other definitions for fetid that I've seen before include "Stinking, rank" , "Smelling bad, stinking" , "Noisome" , "Reeking" , "Having a stale and unpleasant smell" .)