A metal machine operator in America perhaps (6)

I believe the answer is:

nickel

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'a metal' is the definition.
(I know that nickel is a type of metal)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for nickel that I've seen before include "Metal; five US cents" , "Metallic element; US coin" , "Element; five cents in US" , "One twentieth of a US dollar" , "Coin worth half a dime" .)

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

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