If you want stiffening, have a couple! (5)

I believe the answer is:

brace

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'a couple' is the definition.
(brace can mean a pair of something)

I don't understand the remainder of the clue.

(Other definitions for brace that I've seen before include "prepare for impact" , "Pair - wood-boring tool" , "hand tool" , "Pair - strut" , "double" .)

I've seen this clue in the Evening Standard.

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