noun
A light, porous volcanic stone used for scrubbing or as a building material.
かかとの角質を浮き石でこする。
I scrub the calluses on my heels with a pumice stone.
noun
loose rock; loose stone
A rock or stone that is not firmly fixed, often found on slopes or in construction contexts.
登山道には浮き石が多いので注意してください。
Be careful, as there are many loose rocks on the mountain trail.
noun
floating group; group without a base
In the game of Go, a group of stones that lacks a secure base and is vulnerable to attack.
その黒石は浮き石なので、白に攻められやすい。
Those black stones are a floating group, so they are easily attacked by White.
Compound of 浮き (uki, 'floating') + 石 (ishi, 'stone'). The exact historical derivation is uncertain, but the meaning is transparent from its components.