/ Dictionary / Index I ischium: Meaning and Definition of Find definitions for: is•chi•um Pronunciation: (is'kē-um), [key] — pl. -chi•a the lower portion of either innominate bone. See diag. under either of the bones on which the body rests when sitting. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ischium (Thesaurus) Ischia Ischys 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