FeS

from WordNet (r) 3.0 (2006)

Fes
    n 1: a city in north central Morocco; religious center [syn:
         {Fez}, {Fes}]

from The Collaborative International Dictionary of English v.0.48

Troilite \Tro"i*lite\, n. [Named after Dominico Troili, an
   Italian of the 18th century.] (Min.)
   Native iron protosulphide, {FeS}. It is known only in
   meteoric irons, and is usually in imbedded nodular masses of
   a bronze color.
   [1913 Webster]