After polling, understands gains by Labour (5)

I believe the answer is:

earns

I'm a little stuck... Click here to teach me more about this clue!

'gains by labour' is the definition.
(I've seen this before)

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

(Other definitions for earns that I've seen before include "makes money" , "Gains by work" , "Makes - deserves (by one's efforts)" , "Grosses" , "Gains by labour" .)

I've seen this clue in The Telegraph.

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