US explorer wheels about with an inset? (5,4)

I believe the answer is:

human race

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'us' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

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

Can you help me to learn more?

(Other definitions for human race that I've seen before include "Mankind" , "All of us" , "We are all involved" , "Homo sapiens" , "See 8" .)

I've seen this clue in the Sydney Morning Herald.

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