Source : Webster's Revised Unabridged Dictionary (1913)

Jet \Jet\, n. [OF. jet, jayet, F. ja["i]et, 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} (Zo["o]l.), a blackish European ant ({Formica
      fuliginosa}), which builds its nest of a paperlike
      material in the trunks of trees.