Former ingredient of wool dye (3)
I believe the answer is:
'former' is the definition.
(both can mean previous)
'ingredient of wool dye' is the wordplay.
'ingredient of' indicates the answer is hidden within the clue.
'OLD' is hidden in the letters of 'wool dye'.
(Other definitions for old that I've seen before include "Vintage" , "Getting on" , "Ancient" , "Senescent" , "SECOND PART OF 14" .)