| Term | Definition |
| hyperacidity | excessive acidity |
| hypoacidity | weak acidity |
| hyperglycemia | excess of sugar in the blood |
| hypoglycemia | abnormally low level of sugar in the blood |
| hypertension | abnormally high blood pressure |
| hypotension | low blood pressure |
| hyperthermia | especially high fever |
| hypothermia | subnormal body temperature |
| hyperthyroid | (adj) marked by excessive activity of the thyroid gland |
| hypothyroid | (adj) marked by deficient activity of the thyroid gland |
| hyperactive | overactive |
| hyperbole | extravagant exaggeration of statement |
| hypercritical | overcritical |
| hyperemia | suberabundance of blood |
| hyperopia | farsightedness (ant. myopia: nearsightedness) |
| hypersensitive | excessively sensitive |
| hypertrophy | enlargement of a body part or organ, as from excessive use (ant. atrophy: lack of growth from want of nourishment or from disease) |
| hypodermic | injected under the skin |
| hypothesis | theory of supposition assumed as a basis for reasoning |
| hypothetical | assumed without proof for the purpose of reasoning |
| endocrine | secreting internally |
| exocrine | secreting externally |
| endogamy | marriage within the tribe, caste, or social group |
| exogamy | marriage outside the tribe, caste, or social group |
| endogenous | produced from within |
| exogenous | produced from without |
| endoskeleton | internal skeleton or supporting framework in an animal |
| exoskeleton | hard protective structure developed outside the body |
| endosmosis | osmosis inward |
| exosmosis | osmosis outward |
| endocarditis | inflammation of the lining of the heart |
| endoderm | membranelike tissue lining the digestive tract |
| endoparasite | parasite living in the internal organs of animals (ant. ectoparasite: parasite living on the exterior of an animal) |
| endophyte | plant growing within another plant |
| exoteric | external; readily understandable (ant. esoteric) |
| exotic | 1. not native 2. excitingly strange |