marvelous, wonderful, extraordinary, and incredible
massive, ponderous, solid, and substantial
mastery, proficiency, dexterity, and superiority
matchless, unrivaled, inimitable, and incomparable
maxim, proverb, truism, and apothegm [apothegm = terse, witty, instructive saying]
medley, mixture, jumble, and hodge-podge
meekness, inwardness, patience, and self-denial
merciless, remorseless, relentless, and ruthless
mild, gentle, humble, and submissive
mismanagement, indecision, obstinacy, and hardihood