The Collaborative International Dictionary of English v.0.48:
Pebble \Peb"ble\, n. [AS. papolst[=a]n; cf. L. papula pimple,
mote. See Stone.]
1. A small roundish piece of stone; especially, a stone worn
and rounded by the action of water; a pebblestone. "The
pebbles on the hungry beach." --Shak.
As children gathering pebbles on the shore.
2. Transparent and colorless rock crystal; as, Brazilian
pebble; -- so called by opticians.
Pebble powder, slow-burning gunpowder, in large cubical
Scotch pebble, varieties of quartz, as agate, chalcedony,
etc., obtained from cavities in amygdaloid.