A device placed over an animal's snout to prevent biting, barking, or eating. Commonly used for dogs.
散歩のときは犬に口輪を付けてください。
Please put a muzzle on your dog when you take it for a walk.
その犬は口輪
The dog disliked the muzzle and tried to take it off.
Compound of 口 (kuchi, 'mouth') and 輪 (wa, 'ring'). The exact historical derivation is uncertain, but the word transparently describes a ring-like device placed around the mouth.