Pebble
late Old English, recorded as the first element of papel-stān ‘pebble-stone’, pyppelrīpig ‘pebble-stream’, of unknown origin. The word is recorded in place names from the early 12th century onwards.
wiktionary
From Middle English pibel (also in pibleston), from Old English papolstān(“pebble-stone”), from Old English *papol, *pyppel, *pæbbel of unknown origin + Old English stān. Compare Albanian popël. (Can this(+) etymology be sourced?)
etymonline
pebble (n.)
"small, smooth stone," c. 1300, pibel, from Old English papolstan "pebblestone," a word of unknown origin. Perhaps imitative. Some sources compare Latin papula "pustule, pimple, swelling." Historically there is no precise definition based on size other than that it is smaller than a cobble. Related: Pebbly. Pebble-dashing "mortar with pebbles incorporated" is by 1941 (pebble-dash in the same sense is by 1902).