A pinned-on decoration (6)

I believe the answer is:

brooch

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'decoration' is the definition.
(brooch is a kind of decoration)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for brooch that I've seen before include "Decorative pin" , "Breastpin" , "Piece of jewellery" , "Decorative clasp" , "Pinned jewellery item" .)

I've seen this clue in The Globe and Mail.

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