discoidal bead; pierced jade bead
Archaeological term for a type of bead from the Kofun period, often made of jade or similar stone, with a hole through the center.
Many discoidal beads were excavated from this kofun.
Compound of 臼 (usu, 'mortar') and 玉 (tama, 'ball, bead'), referring to the bead's shape. The exact historical derivation is uncertain.