| Term | Definition |
| hyperacidity | excessive acidity |
| hypoacidity | weak acidity |
| hyper | over; above; beyond the ordinary |
| hypo | under; beneath; less than the ordinary |
| 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; hyperpyrexia |
| hypothermia | subnormal body temperature |
| hyperthyroid | marked by excessive activity of the thyroid gland |
| hypothyroid | marked by deficient activity of the thyroid gland |
| hyperactive | overactive |
| hyperbole | extravagant exaggeration of statement |
| hypercritical | overcritical |
| hyperemia | superabundance of blood |
| hyperopia | farsightedness |
| hypersensitive | excessively sensitive; supersensitive |
| hypertrophy | enlargement of a body part or organ, as from excessive use |
| hypodermic | injected under the skin |
| hypothesis | theory or supposition assumed as a basis for reasoning (something "placed under") |
| hypothetical | assumed without proof for the purpose of reasoning; conjectural |