/ Dictionary / Index M mountain beaver: Meaning and Definition of Find definitions for: moun'tain bea"ver Pronunciation: [key] a small, burrowing rodent, Aplodontia rufa, of the Pacific coastal region of North America, considered the most primitive living rodent. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. mountain avens mountain bike Related Content Daily Word Quiz: maritime Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language