Crossword Genius

A popular calling (8)

Ross

I believe the answer is:

nickname

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'a popular calling' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

This is the entire clue.

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(Other definitions for nickname that I've seen before include "tag" , "Friendly appellation by which person is known" , "A handle" , "Cognomen" , "Not the one one is christened with" .)

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