Doubly firm with enthusiast - kind of shy (7)
I believe the answer is:
coconut
'kind of shy' is the definition.
(coconut shy is a traditional game)
'doubly firm with enthusiast' is the wordplay.
'doubly' indicates the doubling of some letters.
'firm' becomes 'co' (abbreviation for company).
'with' is a charade indicator (letters next to each other).
'enthusiast' becomes 'nut' (nut can mean an enthusiast or fan).
'co' doubled is 'coco'.
'coco'+'nut'='COCONUT'
(Other definitions for coconut that I've seen before include "Large palm seed" , "fair target" , "Shy occupier" , "Large edible fruit" , "Flesh" .)