| Term | Description |
| Macle, Mascle | A lozenge-shaped bearing, perforated or vioded. When used in numbers it becomes masculy |
| Manche, Maunch | A bearing representing a sleeve with long hanging ends |
| Mantiger | A monster with the body of a lion or tiger and a human face, usually with a scorpion's tail and long spiral horns. (Also written Mantichor and Manticor.) |
| Marcassin | A young wild boar |
| Marined | An animal having the lower part of the body like a fish |
| Martlet | A fanciful bird somewhat resembling a swallow, but having short tufts of feathers in the place of legs. When used as a difference it denotes the fourth son. |
| Massacre | When the antlers of a stag are attached to a fragnemt of the skull bone it is called a massacre |
| Masoned | Applied to a field or charge which is divided with lines resembling a wall or building of stones |
| Maul | A heavy wooden hammer |
| Membered | A term applied to a bird when its legs are of a different tincture from that of the bird itself. |
| Millrind | A bearing supposed to represent the iron which holds a millstone by being set into its center |
| Moon | The moon in heraldry is always borne as a crescent, usually with the cavity upward. When the cavity is toward the dexter side of the shield, it is increscent; when toward the sinister, decrescent |
| Mooted | Torn up by the roots; eradicated |
| Morne | Without teeth, tongue or claws |
| Mount | The representation of a mound or hill, covered with grass, occupying the base of the shield. It is generally borne with a tree or trees on it. When depicted green it is blazoned as a mount vert. |
| Mullet | bearing resembling a five-pointed star. It is sometimes called a spur rowel, but it was in use long before the rowelled spur. When used as a difference it denotes the third son |
| Muzzled | Having a muzzle. Said of an animal, such as a bear, borne with a muzzle |