tropic

from The Century Dictionary.

• Related to tropine.
• Pertaining to or of the nature of the growing, bending, or moving of organisms in relation to external agents; exhibiting tropism.
• Pertaining to the tropics (the regions so called); tropical.
• noun The turning-point; a solstitial point.
• noun 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.
• noun 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°.
• noun plural With the definite article: the regions lying between the tropics of Cancer and Capricorn, or near them on either side.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Of or pertaining to the tropics; tropical.
• adjective (Zoöl.) any one of three species of oceanic belonging to the genus Phaëthon, found chiefly in tropical seas. They are mostly white, and have two central tail feathers very long and slender. The yellow-billed tropic bird. Phaëthon flavirostris (called also boatswain), is found on the Atlantic coast of America, and is common at the Bermudas, where it breeds.
• adjective (Chem.) Of, pertaining to, or designating, an acid obtained from atropine and certain other alkaloids, as a white crystalline substance slightly soluble in water.
• noun (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.
• noun One of the two parallels of terrestrial latitude corresponding to the celestial tropics, and called by the same names.
• noun The region lying between these parallels of latitude, or near them on either side.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• adjective Of, or relating to the tropics; tropical.
• adjective weather, climate hot and humid.
• adjective biochemistry (noncomparative) Having the quality of indirectly inducing a biological or chemical change in a system or substrate.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective of weather or climate; hot and humid as in the tropics
• noun 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
• adjective relating to or situated in or characteristic of the tropics (the region on either side of the equator)