/ Dictionary / Index N ninetieth: Meaning and Definition of Find definitions for: nine•ti•eth Pronunciation: (nīn'tē-ith), [key] — adj. next after the eighty-ninth; being the ordinal number for 90. being one of 90 equal parts. —n. a ninetieth part, esp. of one (). the ninetieth member of a series. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ninetieth (Thesaurus) nineteenth hole nine-to-five Related Content Daily Word Quiz: impetuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language