Contribution made by fashionable set (5)
I believe the answer is:
input
'contribution' is the definition.
(I've seen this before)
'by fashionable set' is the wordplay.
'by' says to put letters next to each other.
'fashionable' becomes 'in' ('in' can be similar in meaning to 'fashionable').
'set' becomes 'put' ('put' can be a synonym of 'set'**).
'in' put next to 'put' is 'INPUT'.
'made' is the link.
(Other definitions for input that I've seen before include "Resource" , "Data entered to computer" , "Signal supplied to a device" , "Contribution - data fed to computer" , "Signal entering a circuit" .)