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.
      [1913 Webster]

            As children gathering pebbles on the shore.
                                                  --Milton.
      [1913 Webster]

   2. Transparent and colorless rock crystal; as, Brazilian
      pebble; -- so called by opticians.
      [1913 Webster]

   Pebble powder, slow-burning gunpowder, in large cubical
      grains.

   Scotch pebble, varieties of quartz, as agate, chalcedony,
      etc., obtained from cavities in amygdaloid.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pebble \Peb"ble\, v. t. [imp. & p. p. Pebbled; p. pr. & vb. n.
   Pebbling.]
   To grain (leather) so as to produce a surface covered with
   small rounded prominences.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pebble
    n 1: a small smooth rounded rock

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "pebble":
   ace, asphalt, atom, bit, blacktop, carpet, causeway, cement,
   checkstone, cobblestone, concrete, dab, dole, dot, drakestone,
   dram, dribble, driblet, dwarf, farthing, fingerstone, flag, fleck,
   floor, flyspeck, fragment, gobbet, grain, granule, gravelstone,
   groat, hair, handful, iota, jackstone, jot, little, little bit,
   metal, minim, minimum, minutiae, mite, modicum, molecule, mote,
   nutshell, ounce, particle, pave, pebblestone, pinch, pittance,
   point, scruple, slingstone, smidgen, smitch, speck, spoonful, spot,
   tar, thimbleful, tiny bit, tittle, trifling amount, trivia, whit



The Free On-line Dictionary of Computing (30 December 2018):

Pebble

   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)