Foul dictator has lost out (5)

I believe the answer is:

stain

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'foul' is the definition.
(thesaurus)

I don't understand the remainder of the clue.

(Other definitions for stain that I've seen before include "Discoloured mark" , "Tarnish" , "Blemish; colour (wood)" , "Unsightly mark" , "Blotch on satin" .)

I've seen this clue in The Guardian.

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