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Webster 1913 Edition

Noun.

[

Sesqui-

oxide

(Chem.)

An oxide containing three atoms of oxygen with two atoms (or radicals) of some other substance;

thus, alumina,

Al2O3

is a

sesquioxide

sesquioxide ‎(plural sesquioxides)

(chemistry) Any oxide containing three oxygen atoms for every two atoms of another element.

oxide