貝合わせ

Noun



 * 1)  a Heian period game involving matching two pieces of a clamshell
 * 2)  tribadism

Usage notes
The game of kai-awase involves choosing one of two pieces of a clam or other bivalve shell, and attempting to find the matching piece, similar to the game of concentration or pelmanism. A similar image would be painted on each piece of the shell.