/ Dictionary / Index M motor unit: Meaning and Definition of Find definitions for: mo'tor u"nit Pronunciation: [key] a motor neuron and the muscle fibers innervated by its axon. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. motor truck motor van Related Content Daily Word Quiz: perspicacious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language