sandman (n.)

"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.