| Term | Definition |
| hyperacidity | excessive acidity, especially in the stomach |
| hyperactive | excessively active |
| hypercritical | excessively fault-finding; captious |
| hypersensitive | abnormally sensitive |
| hypertension | abnormally high blood pressure |
| hypodemic | small syringe with a hollow needle for making injections beneath the skin |
| hypoglycemic | afflicted with an abnormally low concentration of sugar in the blood |
| hyposensitive | make less sensitive |
| hypotension | abnormally low blood pressure |
| hypothermia | subnormal body temperature |
| subaqueous | underwater |
| subcutaneous | being, living, or introduced beneath the skin |
| sublethal | not quite lethal; insufficient to cause death |
| submarginal | below minimum standards; inadequate for some end; unproductive |
| subservient | useful in an "under" or subordinate, capacity; excessively submissive |
| supererogatory | beyond the requirements of duty; performed to an extent not demanded |
| superficial | over or on the surface only; not profound or thorough |
| supernatural | beyond what is natural or observable; not explained by the laws of nature |
| supernumerary | exceeding the standard or prescribed number; extra |
| supersonic | having a speed beyond that of sound |