Something said about stain (6)
I believe the answer is:
remark
'something said' is the definition.
(a comment or utterance)
'about stain' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'stain' becomes 'mark' (synonyms).
're'+'mark'='REMARK'
(Other definitions for remark that I've seen before include "Notice; happen to say" , "Comment or mention" , "Written or spoken comment" , "Something said; take notice of" , "Observation - notice" .)