Heard Vanish used with jam stain (8)
I believe the answer is:
dyestuff
'stain' is the definition.
(thesaurus)
'heard vanish used with jam' is the wordplay.
'heard' shows a homophone (sound like).
'vanish' becomes 'die' (dying is a kind of vanishing).
'used with' means one lot of letters go next to another.
'jam' becomes 'stuff' (synonyms).
'die' sounds like 'dye'.
'dye'+'stuff'='DYESTUFF'
(Other definitions for dyestuff that I've seen before include "Colourant" , "Colouring agent" , "Substance used in staining" , "Anil perhaps" , "Colouring substance" .)