Intensify a brief moment for lover (7)
I believe the answer is:
'lover' is the definition.
(I know that fanatic is a type of admirer)
'intensify a brief moment' is the wordplay.
'intensify' becomes 'fan' (fanning is a kind of intensifying).
'brief' means to remove the last letter (a shorter or briefer version of the word).
'moment' becomes 'tick' (both can mean a very short amount of time).
'tick' with its last letter taken off is 'tic'.
'for' acts as a link.
(Other definitions for fanatic that I've seen before include "Extreme enthusiast" , "Overzealous person" , "One motivated by irrational enthusiasm" , "Person filled with excessive zeal for cause" , "crank" .)