noun
boulder; cobble; round stone
A naturally rounded stone, often found in rivers or used for decoration. Can refer to stones of various sizes, from small cobbles to large boulders.
川原で大きな丸石を見つけた。
I found a large round stone on the riverbank.
庭に丸石を敷き詰めて小道を作った。
I laid round stones in the garden to make a path.