Jet, n. [OF. jet, jayet, F. jaïet, jais, L. gagates, fr. Gr. �; — so called from � or �, a town and river in Lycia.] [written also jeat, jayet.] (Min.) A variety of lignite, of a very compact texture and velvet black color, susceptible of a good polish, and often wrought into mourning jewelry, toys, buttons, etc. Formerly called also black amber.
Jet ant(Zoöl.), a blackish European ant (Formica fuliginosa), which builds its nest of a paperlike material in the trunks of trees.