Moot vs. Mute
Moral vs. Morale
Morning vs. Mourning
Mortar vs. Mortise
Most vs. Almost
Moat vs. Mote
Motive vs. Motif
Movable vs. Mobile
Multifarious vs. Multitudinous
Munitions vs. Ammunition
Muscle vs. Mussel
Moslem vs. Muslim
Nauseated vs. Nauseous
Noisome vs. Noisy
Nun vs. None
Nutritional vs. Nutritious
Objective vs. Subjective
Obsolescent vs. Obsolete
Official vs. Officious
Ought vs. Aught