"molten rock issuing from a volcano," 1750, from Italian (Neapolitan or Calabrian dialect) lava "torrent, stream," traditionally said to be from Latin lavare "to wash" (from PIE root *leue- "to wash"). Originally applied in Italian to flash flood rivulets after downpours, then to streams of molten rock from Vesuvius. Alternative etymology is from Latin labes "a fall," from labi "to fall, slip" (see lapse (n.)). As an adjective, lavatic (1805), laval (1883). Lava lamp is attested from 1965, also lava light (reg. U.S., 1968, as Lava Lite).