The Collaborative International Dictionary
jayet
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.
Wiktionary
jayet
n. (context obsolete mineralogy English) jet (form of coal)