Inventive fellow to reel it off (7)
I believe the answer is:
fertile
'inventive' is the definition.
(thesaurus)
'fellow to reel it off' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'off' is an anagram indicator.
'reel'+'it'='reelit'
'reelit' is an anagram of 'ertile'.
'f'+'ertile'='FERTILE'
(Other definitions for fertile that I've seen before include "Fruitful" , "(Of soil) richly productive" , "(Of soil) rich" , "Let rife (anag)" , "Highly productive" .)