Piggy bank addition (4)

I believe the answer is:

coin

'piggy bank addition' is the definition.
(I've seen this in another clue)

This is the entire clue.

(Other definitions for coin that I've seen before include "Metal currency" , "Invent a word or phrase - for money?" , "Mint" , "Metal used as money" , "stamp" .)

I've seen this clue in the LA Times and the Newsday.

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