1A stone, rock, or pebble — a hard piece of mineral matter found in nature, such as on the ground or in a riverbed.
川で小さな石をたくさん集めた。
I collected a lot of small stones at the river.
庭に大きな石が置いてある。
There is a large stone placed in the garden.
彼はポケットに石を入れて歩いていた。
He was walking around with a stone in his pocket.
道に石が落ちていたので、よけて歩いた。
There was a stone lying in the road, so I walked around it.
2A jewel or precious stone, such as one set in a ring or necklace.
指輪の石が外れてしまった。
The stone fell out of the ring.
そのネックレスの石は本物のルビーだ。
The stone in that necklace is a real ruby.
この石は誕生石だそうです。
This stone is apparently a birthstone.
3The flint (a small sparking stone) used in lighters to produce a spark; less common today due to the popularity of disposable lighters.
ライターの石を交換する必要がある。
The flint in the lighter needs to be replaced.
4A Go stone — the round black or white piece placed on the board in the game of Go.
彼は慎重に石を置いた。
He placed a stone carefully.
碁の石を黒と白に分けて箱にしまった。
I sorted the Go stones into black and white and put them in the box.
5A hard mass that forms inside the body, such as in the kidney or bladder; a calculus.
医者に腎臓の石が見つかったと言われた。
The doctor told me a kidney stone was found.
痛みがひどくて、石を取り出す手術を受けた。
The pain was severe, so I had surgery to remove the stone.