| 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. |