Fellow on drive turned ardent (6)
I believe the answer is:
fervid
'ardent' is the definition.
(synonyms)
'fellow on drive turned' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'on' means one lot of letters goes inside another.
'turned' indicates anagramming the letters.
'drive' is an anagram of 'ervid'.
'f' inserted into 'ervid' is 'FERVID'.
(Other definitions for fervid that I've seen before include "Zealous" , "Fiery and passionate" , "Intensely enthusiastic" , "Ardent, impassioned" , "Heated - vehement" .)