Skirt for opponent of apartheid (4)

I believe the answer is:

tutu

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'skirt' is the definition.
(I know that tutu is a type of skirt)

I can't explain the rest of the clue.

(Other definitions for tutu that I've seen before include "very short garment" , "Female ballet costume" , "The old primate" , "Giselle's skirt" , "In which dancer may appear" .)

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