Former, past (6)
I believe the answer is:
bygone
I believe this clue is a double definition.
'former' is the first definition.
(I've seen this in another clue)
'past' is the second definition.
(similar in meaning)
(Other definitions for bygone that I've seen before include "Gone by (anag.)" , "Former - well in the past" , "Times past, poetically" , "Erstwhile" , "Olden (days)" .)