jet (n.2)
also jetstone, "deep black lignite," mid-14c., from Anglo-French geet, Old French jaiet "jet, lignite" (12c., Modern French jais), from Latin gagates, from Greek gagates lithos "stone of Gages," town and river in Lycia in Asia Minor. Formerly supposed to be magnetic. From mid-15c. as "a deep, rich, glossy black color" (the color of jet) and as an adjective.
jet (v.2)
"travel by jet," 1946, from jet (n.1). Related: Jetted; jetting.
jet (n.1)
1690s, "stream of water," from French jet "a throw, a cast; a gush, spurt (of water); a shoot (of a plant)," from jeter "to throw, thrust" (from PIE root *ye- "to throw, impel"). Middle English had jet/get "a device, mode, manner, fashion, style" (early 14c.).

Sense of "spout or nozzle for emitting water, gas, fuel, etc." is from 1825. Hence jet propulsion (1855, originally in reference to water) and the noun meaning "airplane driven by jet propulsion" (1944, from jet engine, 1943). The first one in service was the German Messerschmitt Me 262. Jet set first attested 1951, shortly before jet commuter plane flights began. Jet age is attested from 1952. The atmospheric jet stream is from 1947.
jet (v.1)
1690s, "to sprout or spurt forth, shoot out," from French jeter "to throw, thrust," from Late Latin iectare (abstracted from deiectare, proiectare, etc.), in place of Latin iactare "to toss about," frequentative of iacere "to throw, cast," from PIE root *ye- "to throw, impel."

Middle English had a verb getten, jetten meaning "to prance, strut, swagger, be showy" (c. 1400), from getter, jetter, the Old French form of the verb. Related: Jetted; jetting.