Booster (3)
I believe the answer is:
fan
'booster' is the definition.
(I know that fan is a type of enthusiast)
This is all the clue.
(Other definitions for fan that I've seen before include "Spanish women wave it to cool themselves" , "Keen follower; cooler" , "Cooling device for enthusiastic supporter" , "Cool - enthusiast" , "Cooling device or disciple of performer" .)