Back-to-the-past style (5)
I believe the answer is:
retro
'back-to-the-past style' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for retro that I've seen before include "Consciously old style" , "Imitative of past styles" , "Imitative of an older style" , "Reminiscent of a past style" , "reminding us of the past" .)