Fan of Greek character tense (3)
I believe the answer is:
nut
'fan' is the definition.
(both can mean an enthusiast)
'greek character tense' is the wordplay.
'greek character' becomes 'nu' (Greek letter).
'tense' becomes 't' (grammatical abbreviation).
'nu'+'t'='NUT'
'of' is the link.
(Other definitions for nut that I've seen before include "Vegetarian food" , "Head; hard fruit" , "Hard-skinned fruit" , "keen admirer" , "One securing bolt" .)