Trainee left with one bringing home the bacon? (7)

I believe the answer is:

learner

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'trainee' is the definition.
(thesaurus)

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

(Other definitions for learner that I've seen before include "One who studies" , "Acquirer of knowledge" , "Pupil or apprentice" , "Trainee (driver)" , "One under tuition" .)

I've seen this clue in The Telegraph.

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