sandbar (n.)

late 12c., "stake or rod of iron used to fasten a door or gate," from Old French barre "beam, bar, gate, barrier" (12c.), from Vulgar Latin *barra "bar, barrier," which some suggest is from Gaulish *barros "the bushy end" [Gamillscheg, etc.], but OED regards this as "discredited" because it "in no way suits the sense." Welsh bar "a bar, rail," Irish barra "a bar, spike" are said to be from English; German Barre, Danish barre, Russian barŭ are from Medieval Latin or Romanic. 

The general sense of "anything which obstructs, hinders, or impedes" is from 1530s. Of soap, by 1833; of candy, by 1906 (the process itself dates to the 1840s), both from resemblance of shape. The meaning "bank of sand across a harbor or river mouth" is from 1580s, probably so called because it was an obstruction to navigation.

Bar graph is attested from 1925. Bar code first recorded 1963. Behind bars "in prison" is attested by 1934, American English.

"water-worn detritus finer than gravel; fine particles of rocks (largely crystalline rocks, especially quartz); the material of the beach, desert, or sea-bed;" Old English sand, from Proto-Germanic *sandam (source also of Old Norse sandr, Old Frisian sond, Middle Dutch sant, Dutch zand, German Sand), cognate with Greek psammos "sand;" Latin sabulum "coarse sand" (which is the source of Italian sabbia, French sable). This was said to be from a suffixed form of a PIE root *bhes- "to rub," but de Vaan says the Latin is from a substrate word and Beekes suggests for the origin of psammos "Pre-Greek *sam- 'sand, mud'."

Historically, the line between sand and gravel was not distinct. A general Germanic word but it is not attested in Gothic, which used in this sense malma, related to Old High German melm "dust" and the first element of the Swedish city name Malmö (the second element meaning "island"), and to Latin molere "to grind."

Sand has been a figure of innumerability or instability since Old English. In compounds, often it indicates "of the shore, found on sandy beaches." The old U.S. colloquial sense of "grit, endurance, pluck" is by 1867, especially in have sand in (one's) craw. Sands "tract or region composed of sand," is by mid-15c.