/ Dictionary / Index O ostium: Meaning and Definition of Find definitions for: os•ti•um Pronunciation: (os'tē-um), [key] — pl. -ti•a a small opening or orifice, as at the end of the oviduct. one of the tiny holes in the body of a sponge. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. ostiole ostler Related Content Daily Word Quiz: acquiesce Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language