Concise Oxford English Dictionary
muzzle
■ noun
the projecting part of the face, including the nose and mouth, of an animal such as a dog or horse. ▶a guard fitted over an animal’s muzzle to stop it biting or feeding.
the open end of the barrel of a firearm.
■ verb
put a muzzle on (an animal).
prevent from freedom of expression.

ME: from OFr. musel, dimin. of med. L. musum.
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Concise Oxford Thesaurus
muzzle
▶ noun the dog’s velvety muzzle: SNOUT, nose, mouth, maw.
▶ verb attempts to muzzle the media: GAG, silence, censor, stifle, restrain, check, curb, fetter.
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Merriam-Webster Collegiate® Dictionary
1muz·zle
Pronunciation: ‘mə-zəl
Function: noun
Etymology: Middle English mosel, from Middle French musel, from Old French *mus mouth of an animal, from Medieval Latin musus
Date: 15th century

1 : the projecting jaws and nose of an animal : SNOUT
2 a : a fastening or covering for the mouth of an animal used to prevent eating or biting b : something (as censorship) that restrains normal expression
3 : the open end of an implement especially : the discharging end of a weapon

muzzle[1] 2muzzle
Function: transitive verb
Inflected Form: muz·zled ; muz·zling \’məz-liŋ, ‘mə-zə-\
Date: 15th century

1 : to fit with a muzzle
2 a : GAG b : RESTRAIN, RESTRICT –muz·zler \-lər\ noun