Erstwhile, former (3)
I believe the answer is:
old
This clue is a double definition.
'erstwhile' is the first definition.
(I've seen this in another clue)
'former' is the second definition.
(both can mean previous)
(Other definitions for old that I've seen before include "Advanced in years" , "Obsolete" , "Getting on" , "SECOND PART OF 14" , "Much-used" .)