/ Dictionary / Index S sesquioxide: Meaning and Definition of Find definitions for: ses•qui•ox•ide Pronunciation: (ses"kwē-ok'sīd, -sid), [key] — n. Chem. an oxide containing three atoms of oxygen and two of another element, as aluminum oxide, AlO. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. sesquicentennial sesquipedalian Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language