n (uncountable) Rock that is ground more finely than gravel, but is not as fine as silt (more formally, see w:Particle size (grain size)|grain sizes chart), forming beaches and deserts and also used in construction.
n (uncountable|geology) A particle from 62.5 microns to 2 mm in diameter, following the Wentworth scale.
v (transitive) To abrade the surface of (something) with sand or sandpaper in order to smooth or clean it.