/ Dictionary / Index L lumbar plexus: Meaning and Definition of Find definitions for: lum'bar plex'us Pronunciation: [key] — Anat. Anat. a network of nerves originating in the spinal nerves of the midback region and innervating the pelvic area, the front of the legs, and part of the feet. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. lumbar lumbar puncture Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language