/ Dictionary / Index M M-line: Meaning and Definition of Find definitions for: M-line Pronunciation: (em'līn"), [key] — n. Physics. one of a series of linesin the x-ray spectrum of an atom corresponding to radiationcaused by the transition of an electron to the M-shell. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. MLG. Mlle. Related Content Daily Word Quiz: nonchalant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language