One enthusiast accepts penny contribution (5)
I believe the answer is:
input
'contribution' is the definition.
(input means someone's contribution to something)
'one enthusiast accepts penny' is the wordplay.
'one' becomes 'i' (Roman numeral).
'enthusiast' becomes 'nut' (nut can mean an enthusiast or fan).
'accepts' indicates putting letters inside.
'penny' becomes 'p' (short for pence).
'nut' placed around 'p' is 'nput'.
'i'+'nput'='INPUT'
(Other definitions for input that I've seen before include "contributed information" , "Signal feeding a circuit" , "Data entered to computer" , "Contributory remark(s)" , "Signal entering a circuit" .)