Pebble

A pebble is a clast of rock with a particle size of 4 to 64 millimeters based on the Krumbein phi scale of sedimentology. A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history. They have been found at Olduvai Gorge (1.85 million years ago) and at Longuopo in China (1.8 to 1.5 MYA).
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(v. t.)
To grain (leather) so as to produce a surface covered with small rounded prominences.
  

(n.)
Transparent and colorless rock crystal; as, Brazilian pebble; -- so called by opticians.
  

(n.)
A small roundish stone or bowlder; especially, a stone worn and rounded by the action of water; a pebblestone.
  

A polymorphic language.
["A Kernel Language for Abstract Data Types and Modules", R.M. Burstall & B. Lampson, in Semantics of Data Types, LNCS 173, Springer 1984].
(1995-01-26)

Noun
1. a small smooth rounded rock
(hypernym) rock, stone