Enthusiast somewhat diminutive (3)
I believe the answer is:
nut
'enthusiast' is the definition.
(nut can mean an enthusiast or fan)
'somewhat diminutive' is the wordplay.
'somewhat' indicates a hidden word.
'NUT' can be found hidden inside 'diminutive'.
(Other definitions for nut that I've seen before include "Hard edible seed" , "Brazil, for instance" , "eg Almond, brazil" , "Headcase" , "Fruitcake" .)