Hill worker (3)

I believe the answer is:

ant

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This could be a double definition.

'hill' is the first definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

'worker' is the second definition.
(worker is a type of ant)

Can you help me to learn more?

(Other definitions for ant that I've seen before include "Little boy" , "Industrious insect" , "Small social insect" , "Termite" , "One working hard" .)

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

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