Stained form as a substitute (7)
I believe the answer is:
instead
'as a substitute' is the definition.
(I've seen this in another clue)
'stained form' is the wordplay.
'form' indicates an anagram (a different form of the same letters).
'stained' with letters rearranged gives 'INSTEAD'.
(Other definitions for instead that I've seen before include "In place (of)" , "for a change" , "as an alternative option" , "Rather - detains (anag)" , "In lieu" .)