Crossword Genius

Silly repetition? (4)

Ross

I believe the answer is:

gaga

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'silly' is the definition.
(thesaurus)

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

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(Other definitions for gaga that I've seen before include "Slang for crazy - apply a gag" , "Slangily and repetitively crazy" , "bananas" , "Lady who sings" , "Senile or crazy in repetitive way" .)

I've seen this clue in the Evening Standard.
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