Clothing that may be the rage (4)
I believe the answer is:
gear
'clothing' is the definition.
(gear can informally mean clothing)
'may be the rage' is the wordplay.
'may be' indicates an anagram.
'rage' with letters rearranged gives 'GEAR'.
'that' acts as a link.
(Other definitions for gear that I've seen before include "Toothed wheel and youthful fashion" , "Cogwheel - equipment" , "Equipment, clothing, goods" , "Toothed wheel which engages with another one" , "often changed in a saloon" .)