noun
kai-awase; shell-matching game
A Heian-period court game where players match pairs of clam shells by their unique patterns. Sense 2 is a historical variant emphasizing the comparison aspect.
貝合わせは平安時代の貴族の遊びです。
Kai-awase is a game played by Heian-period aristocrats.
noun
tribadism; tribbing
Colloquial and vulgar term for a sexual act between women, derived from the image of shells rubbing together.
その単語は俗語で、貝合わせという表現が使われることがある。
That word is slang, and the expression 貝合わせ is sometimes used.
A broader term for matching games; 貝合わせ is a specific type using shells.
Compound of 貝 (kai, 'shell') and 合わせ (awase, 'matching'). The vulgar sense is a metaphorical extension based on the shape and rubbing motion of shells.