| morass | An area of muddy or boggy ground | |
| morbid | Characterized by an abnormal and unhealthy interest in disturbing and unpleasant subjects, especially death and disease | |
| mordant | Having or showing a sharp or critical quality; biting | |
| mores | The essential or characteristic customs and conventions of a community | |
| moribund | At the point of dying; in terminal decline—lacking vitality or vigor | |
| morose | Sullen and ill-tempered | |
| motile | Capable of movement | |
| motley | Exhibiting great diversity of elements; being of different colors combined | |
| multifaceted | Having many aspects or sides | |
| munificent | Very generous | |