Deputy capable of some circumlocution (5)

I believe the answer is:

locum

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'deputy' is the definition.
(both can mean a substitute or stand-in)

I cannot understand how the rest of the clue works.

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(Other definitions for locum that I've seen before include "Medical temp?" , "Professional who stands in for another" , "Temporary deputy for doctor" , "Professional who substitutes temporarily for another" , "A substitute or stand-in doctor" .)

I've seen this clue in the Evening Standard.

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