Guinea inferior to former French colony? That's slander (6)

I believe the answer is:

malign

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'that's slander' is the definition.
(maligning is a kind of slandering)

I don't understand how the rest of the clue works.

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(Other definitions for malign that I've seen before include "Laming in harmful way" , "Vilify, denigrate." , "Say unpleasant and untrue things about" , "Evil, baleful" , "Speak bad of" .)

I've seen this clue in The Guardian.

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