| Term | Definition |
| homo | Greek root: one and the same, like |
| hetero | Greek root: different |
| homochromatic | having the same color |
| heterochromatic | having different colors |
| homogeneous | of the same kind, similar, uniform |
| heterogeneous | differing in kind, dissimilar, varied |
| homology | fundamental similarity of structures |
| heterology | lack of correspondence between parts |
| homomorphic | exhibiting similarity of form |
| heteromorphic | exhibiting diversity of form |
| homonym | word that sounds like another but differs in meaning and spelling |
| heteronym | word spelled like another but differing in sound and meaning |
| homocentric | having the same center, concentric |
| homophonic | having the same sound |
| heteroclite | deviating from the common rule, abnormal, atypical or person or thing deviating from the common rule |
| heterodox | opposed to accepted beliefs or established doctrines, unorthodox |
| hyper | greek root: over, above, beyond the ordinary |
| hypo | greek root: under, beneath, less than the ordinary |
| 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, 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 |
| hypothetical | assumed without proof for the purpose of reasoning, conjectural |