jet \jet\, n. of. jet, jayet, f. ja"iet, 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.
   1913 webster

   jet ant zool., a blackish european ant formica
      fuliginosa, which builds its nest of a paperlike
      material in the trunks of trees.
      1913 webster
see also:
jeat jayet black amber jet ant formica fuliginosa