Relative is mostly vague (5)

I believe the answer is:

uncle

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'relative' is the definition.
(uncle is a kind of relative)

I can't explain the rest of the clue.

(Other definitions for uncle that I've seen before include "one who's taken the pledge" , "Family relation" , "Brother of one's parent" , "older relative" , ". . . . . Sam, the US government" .)

I've seen this clue in The Mirror.

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