Bracer, often after a gin (5)

I believe the answer is:

tonic

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'bracer' is the definition.
(thesaurus)

I don't understand the rest of the clue.

(Other definitions for tonic that I've seen before include "An enlivener" , "Gin mixer - pick-me-up" , "shot in the arm" , "Producing tension of muscles" , "It goes with gin" .)

I've seen this clue in The Mirror.

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