tropic

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Either of two parallels of latitude on the earth, one 23°27ʹ north of the equator and the other 23°27ʹ south of the equator, representing the points farthest north and south at which the sun can shine directly overhead and constituting the boundaries of the Torrid Zone.
2. n. The region of the earth's surface lying between these latitudes.
3. n. Astronomy Either of two corresponding parallels of celestial latitude that are the limits of the apparent northern and southern passages of the sun.
4. adj. Of or relating to the Tropics; tropical.

Century Dictionary and Cyclopedia

1. Pertaining to or of the nature of the growing, bending, or moving of organisms in relation to external agents; exhibiting tropism.
2. Related to tropine.
3. Pertaining to the tropics (the regions so called); tropical.
4. n. The turning-point; a solstitial point.
5. n. In astronomy, one of two circles on the celestial sphere whose distances from the equator are each equal to the obliquity of the ecliptic, or 23½° nearly. The northern one touches the ecliptic at the sign Cancer, and is thence called the tropic of Cancer, the southern one being for a similar reason called the tropic of Capricorn. The sun's annual path in the heavens is bounded by these two circles, and they are called tropics because when the sun, in his journey northward or southward, reaches either of them, he, as it were, turns back, and travels in an opposite direction in regard to north and south.
6. n. In geography, one of two parallels of latitude, each at the same distance from the terrestrial equator as the celestial tropics are from the celestial equator—that is, about 23½°. The one north of the equator is called the tropic of Cancer, and that south of the equator the tropic of Capricorn. Over these circles the sun is vertical when his declination is greatest, and they include the part of the globe called the torrid zone—a zone 47° in width, having the equator for its central line.
7. n. plural With the definite article: the regions lying between the tropics of Cancer and Capricorn, or near them on either side.

Wiktionary

1. 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.
2. adj. Of, or relating to the tropics; tropical.
3. adj. weather, climate hot and humid.
4. adj. biochemistry (noncomparative) Having the quality of indirectly inducing a biological or chemical change in a system or substrate.

GNU Webster's 1913

1. adj. (Chem.) Of, pertaining to, or designating, an acid obtained from atropine and certain other alkaloids, as a white crystalline substance slightly soluble in water.
2. n. (Astron.) One of the two small circles of the celestial sphere, situated on each side of the equator, at a distance of 23° 28′, and parallel to it, which the sun just reaches at its greatest declination north or south, and from which it turns again toward the equator, the northern circle being called the Tropic of Cancer, and the southern the Tropic of Capricorn, from the names of the two signs at which they touch the ecliptic.
3. n. One of the two parallels of terrestrial latitude corresponding to the celestial tropics, and called by the same names.
4. n. The region lying between these parallels of latitude, or near them on either side.
5. adj. Of or pertaining to the tropics; tropical.

WordNet 3.0

1. adj. of weather or climate; hot and humid as in the tropics
2. n. either of two parallels of latitude about 23.5 degrees to the north and south of the equator representing the points farthest north and south at which the sun can shine directly overhead and constituting the boundaries of the Torrid Zone or tropics
3. adj. relating to or situated in or characteristic of the tropics (the region on either side of the equator)