The most common and most likely answer to this crossword clue is the 6 letter word MUZZLE
I've seen this crossword clue in The Times
M
U
Z
Z
L
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More clues leading to the result MUZZLE
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The straight part
We know that "gag" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gag = muzzle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MUZZLE mean?
MUZZLE noun- The protruding part of an animal's head which includes the nose, mouth and jaws; the snout
- The mouth or the end for entrance or discharge of a gun, pistol etc., that the bullet emerges from as opposed to the breech.
- A device used to prevent animal from biting or eating, which is worn on its snout.
- A piece of the forward end of the plow-beam by which the traces are attached; bridle
- An openwork covering for the nose, used for the defense of the horse, and forming part of the bards in the 15th and 16th centuries.
- To bind or confine an animal's mouth by putting a muzzle, as to prevent it from eating or biting.
- To restrain (from speaking, expressing opinion or acting); gag, silence, censor.
- To veil, mask, muffle.
- To fondle with the closed mouth; to nuzzle.
- To bring the muzzle or mouth near.