Stained form as a substitute (7)
I believe the answer is:
instead
'as a substitute' is the definition.
(I've seen this before)
'stained form' is the wordplay.
'form' is an anagram indicator (another form of the 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" .)