/ Dictionary / Index N Nios: Meaning and Definition of Find definitions for: Ni•os Pronunciation: (nē'ōs), [key] — n. a volcanic lake in Cameroon, at the NW border: eruption 1986. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. Niort NIOSH Related Content Daily Word Quiz: secular Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language