/ Dictionary / Index R rivulus: Meaning and Definition of Find definitions for: riv•u•lus Pronunciation: (riv'yu-lus), [key] — pl. -lus. any of several killifishes of the genus Rivulus, native to small streams of tropical America, often kept in aquariums. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: rivulus (Thesaurus) rivulet rix-dollar Related Content Daily Word Quiz: torrid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language