Crossword Genius

Merchant's partner's material stolen from 1D (5)

Ross

I believe the answer is:

ivory

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'merchant's' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for ivory that I've seen before include "Jumbo's dentine" , "National emblem" , "Elephant tusk material" , "pasty" , "Film director" .)

I've seen this clue in The Independent.
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