Lodger finds boundary we hear (7)

I believe the answer is:

boarder

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'lodger' is the definition.
(synonyms)

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

(Other definitions for boarder that I've seen before include "Pupil who lives in school" , "Residential pupil" , "Lodger - invader of boat" , "Pupil living at school" , "Resident pupil" .)

I've seen this clue in The Sun.

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