Clothing that's back in starts off all the rage (6)
I believe the answer is:
attire
'clothing' is the definition.
(attire is a kind of clothing)
'that's back in starts off all the rage' is the wordplay.
'back' says to take the final letters (the letter at the back).
'in' means one lot of letters goes inside another.
'starts off' says to take the initial letters.
'rage' becomes 'ire' (ire is intense rage).
The last letter of 'that' is 't'.
The initial letters of 'all the' is 'at'.
't' going within 'at' is 'att'.
'att'+'ire'='ATTIRE'
(Other definitions for attire that I've seen before include "Habit" , "Formal dress or costume" , "Wear" , "Special clothing" , "Garments" .)