/ Dictionary / Index S semiquinone: Meaning and Definition of Find definitions for: sem•i•qui•none Pronunciation: (sem"ē-kwi-nōn', -kwin'ōn, sem"ī-), [key] — n. Chem. any of the class of free radicals formed as intermediates in the oxidation of a hydroquinone to a quinone. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. semiquaver Semiramis Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language