| Tropic | |
| 1. n. alternative form of tropic (one of two specific lines of latitude that divide the Northern and Southern hemispheres, respectively; the Tropic of Cancer and the Tropic of Capricorn). | |
| 2. n. either of the two parallels of latitude 23°27′ north and south of the equator; the farthest points at which the sun can be directly overhead; the boundaries of the torrid zone or tropics | |
| 3. adj. Of, or relating to the tropics; tropical. | |
| 4. adj. (weather, climate) hot and humid. | |
| 5. adj. (biochemistry) (noncomparative) Having the quality of indirectly inducing a biological or chemical change in a system or substrate. | |
| The binding of oxygen to hemoglobin is allosterically regulated by various tropic factors, such as BPG and acidity. | |
