noun
A metal mouthpiece used to control a horse, placed in the mouth and attached to the bridle. The word is usually written in kana.
See also: 轡
馬にはみを噛ませてから乗り始めた。
I put the bit in the horse's mouth before starting to ride.
はみが合わないと馬が嫌がることがある。
If the bit doesn't fit well, the horse may resist.
Rare kanji spelling; the reading はめ is also possible but less common.
轡 refers to the entire bridle or the bit with its side rings, while はみ specifically means the mouthpiece itself.
The origin is uncertain; the word is native Japanese. The kanji 馬銜 literally means 'horse hold in mouth', but the kana spelling is standard.