a small smooth rounded rock
"She carefully selected a perfectly round pebble from the riverbed to use as a paperweight."
A small stone, especially one rounded by the action of water.
"She carefully placed the smooth pebble she had found along the riverbank into her collection jar."
To pave with pebbles.
"The old lane has been re-paved with smooth river pebbles to create a charming, rustic pathway."