| Term | Definition |
| A (AN) | not, without |
| Amoral | not moral; without sense of moral responsibility |
| Amorphous | without definite form or shape |
| Anarchy | total absence of rule of government; confusion; disorder |
| Anemia | lack of normal number of red blood cells |
| Anesthesia | loss of feeling or sensation resulting from ether, chloroform, Novocain, etc. |
| Anesthetic | drug that produces anesthesia |
| Anomalous | not normal; abnormal |
| Anomaly | one that is peculiar, irregular, abnormal, or difficult to classify |
| Anonymous | nameless; of unknown or unnamed origin |
| Anoxia | condition characterized by an absence of oxygen supply to an organ or a tissue |
| Apnea | temporary absence or cessation of breathing |
| Aseptic | free from disease-causing microorganisms |
| Asymptomatic | showing no symptoms of disease |
| Atheism | godlessness; denial in the existence of a Supreme Being |
| Atrophy | a wasting or decrease in size of a body organ, tissue, or part owing to disease, injury, or lack of use |
| Atypical | unlike the typical |
| MONO (MON) | one, single, alone |
| POLY | many |
| Monarchy | ruled by a single person |
| Polyarchy | ruled by many |
| Monochromatic | of one color |
| Polychromatic | showing a variety of colors |
| Monogamy | marriage with one mate at a time |
| Polygamy | marriage to several mates at the same time |
| Monomorphic | having a single form |
| Polymorphic | having various forms |
| Monosyllabic | having one syllable |
| Polysyllabic | have more than one syllable |
| Monotheism | belief that there is one god |
| Polytheism | belief that there is more than one god |
| Monocle | eyeglass for one eye |
| Monogram | two or more letters interwoven to represent a name |
| Monograph | a detailed written study of a single specialized subject or an aspect of it |
| Monologue | long speech given by one person |
| Monomania | exaggerated or obsessive enthusiasm for or preoccupation with one thing. |
| Polyglot | person who speaks several languages |
| Polyphonic | having many sounds or voices |