Foul dictator has lost out (5)
I believe the answer is:
stain
'foul' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for stain that I've seen before include "Discoloured mark" , "Tarnish" , "Blemish; colour (wood)" , "Unsightly mark" , "Blotch on satin" .)