kai-awase
貝合わせ
A concentration game with clamshells that started in the Heian period. It was originally called Kai-Ooi (貝覆い) and later called Kai-Awase in the Edo period. However, the word is frequently used as a slang term for "tribadism".
See also
* Wikipedia article (JP)
* Tag_Group:Board(?)_Games