Spot ruining satin (5)
I believe the answer is:
stain
'spot' is the definition.
(synonyms)
'ruining satin' is the wordplay.
'ruining' indicates anagramming the letters.
'satin' is an anagram of 'STAIN'.
(Other definitions for stain that I've seen before include "Blemish; colour (wood)" , "Stigma" , "Penetrative dye; mark" , "Discoloration" , "Satin (anag.)" .)