Roman garment of past time on the way back (4)
I believe the answer is:
toga
'roman garment' is the definition.
(I've seen this before)
'past time on the way back' is the wordplay.
'past' becomes 'ago' ('ago' can be similar in meaning to 'past').
'time' becomes 't'.
'on the way back' is a reversal indicator.
'ago'+'t'='agot'
'agot' in reverse letter order is 'TOGA'.
'of' acts as a link.
(Other definitions for toga that I've seen before include "Outer garment" , "Old Roman gown" , "Robe worn by Caesar" , "Roman male garb" , "Classical garment" .)