| Term | Definition |
| Monograph | learned treatise on a particular subject; scholarly article |
| Monologue | lengthy talk by one person |
| Monorail | railway whose cars are supported on a single rail |
| Monosyllabic | having only one syllable |
| Monotonous | tiresome becuase of lack of variety |
| Multifaceted | having many facets or aspects |
| Multilateral | having many sides; participated in by more than two participants |
| Multimedia | involving the use of two or more media, such as slides, films, tape recordings, flashing colored lights, etc. |
| Multinational | having subsidairies or operations in several countries |
| Polygamist | person married to two or more mates at the same time |
| Polygot | person who speaks or writes several languages |
| Polymath | person of great and diversified learning |
| Polytechnic | providing instruction in many technical arts and applied sciences |
| Polytheistic | believing in more than one god |
| Unanimous | being of one and the same opinion; showing complete agreement |
| Unicameral | consisting of or having one legislative chamber |
| Uniform | always the same; not varying in form, degree, or manner |
| Unilateral | involving or affecting one side only; one-sided |
| Unique | being the only one of its kind; highly unusual |
| Unisex | not distinguishable as male or female; designed for both sexes |
| Monarchy | a government with one hereditary ruler |
| Monastery | dwelling place for monks living secluded from the world |
| Monocle | an eyeglass for one eye |
| Monogamy | marriage to only one person at a time |
| Monolith | one single large piece of stone, as a monument or statue |
| Monopoly | exclusive control by one group of a commodity or sevice |
| Monosyllable | a word of one syllable |
| Monotheism | the belief that there is only one God |
| Monotone | having one tone; lack of variety of tone |