A sasso (stone) that has been made smooth and round by the action of water is a ciottolo (pebble) in Italian. It is the diminutive form of ciotto, an archaic word for pebble.

Ciottolo is a masculine noun whose plural form is ciottoli. The definite and indefinite articles it takes are as follows:
- il ciottolo = the pebble
- i ciottoli = the pebbles
- un ciottolo = a pebble
- dei ciottoli = (some) pebbles
Prese un ciottolo e lo gettò nell’acqua.
He picked up a pebble and threw it in the water.

Here are three of the most common types of pebbles:
- ciottolo della spiaggia = beach pebble
- ciottolo del torrente = stream pebble
- ciottolo del fiume = river pebble
Note: Ciottolo should not be confused with the similar sounding ciotola which means bowl or dish!
The adjective ciottoloso means pebbly, but when used to refer to the surface of a path or road, it translates as cobblestone. For example, a cobblestone road would be una strada a ciottoli.
In Tuscany, ciottolo is also the word for a terracotta dish.