noun
small opening under the sleeve of traditional Japanese clothing
Refers to the opening where the sleeve meets the bodice, below the armpit, found on kimono and yukata for women and children. A specialized term used in clothing contexts.
子供の浴衣には身八つ口がある。
Children's yukata have a small opening under the sleeve.
身八つ口から手を入れて帯を直す。
I adjust the obi by putting my hand through the opening under the sleeve.
Refers to the opening at the sleeve end (cuff) of traditional clothing, whereas 身八つ口 is the opening under the armpit where the sleeve meets the bodice.
Compound of 身 (mi, 'body') + 八つ (yatsu, 'eight') + 口 (kuchi, 'opening'). The exact origin of 'eight' is uncertain, but it may refer to the number of openings in traditional clothing or be a phonetic element.