Sesquioxide
Pronunciation : Ses`qui*ox"ide
Part of Speech : n.
Etymology : [Sesqui- + oxide.] (Chem.)
Definition : Defn: An oxide containing three atoms of oxygen with two atoms (or radicals) of some other substance; thus, alumina, Al2O3 is a sesquioxide.
Source : Webster's Unabridged Dictionary, 1913