/ Dictionary / Index S semidiurnal: Meaning and Definition of Find definitions for: sem•i•di•ur•nal Pronunciation: (sem"ē-dī-ûr'nl, sem"ī-), [key] — adj. pertaining to, consisting of, or accomplished in half a day. occurring every 12 hours or twice each day. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. semidiameter semidivine Related Content Daily Word Quiz: fidelity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language