Crossword Genius

Key material for piano makers (5)

Ross

I believe the answer is:

ivory

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'key material' is the definition.
(I've seen this before)

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

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(Other definitions for ivory that I've seen before include "Hard creamy-white dentine used for making ornaments" , "Substance of elephant's tusk" , "Key perhaps" , "Creamy colour" , "What may be carved" .)

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