noun
small opening under the sleeve of traditional Japanese clothing
Refers to the slit or opening where the sleeve meets the bodice, below the armpit, found in garments like kimono or yukata. A specialized term used mainly in the context of traditional clothing.
着物の八つ口から風が入って涼しい。
The breeze comes in through the opening under the sleeve of the kimono, making it cool.
八つ口の縫い方が少しほつれている。
The stitching of the underarm opening is coming undone a little.
The term 八つ口 (やつくち) literally means 'eight mouths' or 'eight openings', but the exact origin of the name is uncertain. It may refer to the shape or the number of openings in traditional clothing, though this is speculative.