Polly can only tell you what she's heard (6)

I believe the answer is:

parrot

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'polly' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

(Other definitions for parrot that I've seen before include "Psittacine bird" , "Bright tropical bird" , "Brightly coloured bird that mimics speech" , "Eg, macaw" , "Bird (that repeats)" .)

I've seen this clue in the Evening Standard.

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