Former ingredient in wool dyeing (3)
I believe the answer is:
old
'former' is the definition.
(both can mean previous)
'ingredient in wool dyeing' is the wordplay.
'ingredient in' says the answer is hidden in the clue (I've seen 'ingredients in' mean this).
'OLD' is hidden within 'wool dyeing'.
(Other definitions for old that I've seen before include "Advanced in years" , "Stale" , "Obsolete" , "SECOND PART OF 14" , "Former; aged" .)