- metropolis: A chief city, either the capital or the largest or most important city of a state.
- metropolitan: Pertaining to a chief city.
- mettle: Courage.
- mettlesome: Having courage or spirit.
- microcosm: The world or universe on a small scale.
- micrometer: An instrument for measuring very small angles or dimensions.
- microphone: An apparatus for magnifying faint sounds.
- microscope: An instrument for assisting the eye in the vision of minute objects or features of objects.
- microscopic: Adapted to or characterized by minute observation.
- microscopy: The art of examing objects with the microscope.
- midsummer: The middle of the summer.
- midwife: A woman who makes a business of assisting at childbirth.
- mien: The external appearance or manner of a person.
- migrant: Wandering.
- migrate: To remove or pass from one country, region, or habitat to another.
- migratory: Wandering.
- mileage: A distance in miles.
- militant: Of a warlike or combative disposition or tendency.
- militarism: A policy of maintaining great standing armies.
- militate: To have weight or influence (in determining a question).
- militia: Those citizens, collectively, who are enrolled and drilled in temporary military organizations.
- Milky Way: The galaxy.
- millet: A grass cultivated for forage and cereal.
- mimic: To imitate the speech or actions of.
- miniature: Much smaller than reality or that the normal size.
- minimize: To reduce to the smallest possible amount or degree.
- minion: A servile favorite.
- ministration: Any religious ceremonial.
- ministry: A service.
- minority: The smaller in number of two portions into which a number or a group is divided.
- minute: Exceedingly small in extent or quantity.
- minutia: A small or unimportant particular or detail.
- mirage: An optical effect looking like a sheet of water in the desert.
- misadventure: An unlucky accident.
- misanthropic: Hating mankind.
- misanthropy: Hatred of mankind.
- misapprehend: To misunderstand.
- misbehave: To behave ill.
- misbehavior: Ill or improper behavior.
- mischievous: Fond of tricks.
- miscount: To make a mistake in counting.
- miscreant: A villain.
- misdeed: A wrong or improper act.
- misdemeanor: Evil conduct, small crime.
- miser: A person given to saving and hoarding unduly.
- mishap: Misfortune.
- misinterpret: To misunderstand.
- mislay: To misplace.
- mismanage: To manage badly, improperly, or unskillfully.
- misnomer: A name wrongly or mistakenly applied.