Such a porter may be stout (6)

I believe the answer is:

strong

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'be stout' is the definition.
(thesaurus)

I can't explain the remainder of the clue.

(Other definitions for strong that I've seen before include "is excelling" , "Physically powerful - feel 1 Across" , "strong" , "firm" , "Mighty, powerful" .)

I've seen this clue in the Evening Standard.

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