Source : Webster's Revised Unabridged Dictionary (1913)

Sesquisulphide \Ses`qui*sul"phide\, n. [Sesqui- + sulphide.]
   (Chem.)
   A sulphide, analogous to a sesquioxide, containing three
   atoms of sulphur to two of the other ingredient; -- formerly
   called also {sesquisulphuret}; as, orpiment, {As2S3} is
   arsenic sesquisulphide.