Has two ways of ensuring silence? (3)

I believe the answer is:

gag

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'silence?' is the definition.
(gagging is a kind of silencing)

I don't understand how the rest of the clue works.

(Other definitions for gag that I've seen before include "Retch at the joke?" , "Joke, hoax" , "Funny" , "A palindromic joke or muzzle" , "that renders one speechless" .)

I've seen this clue in the Evening Standard.

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