(trop′ik) noun
1. Geog. Either of two parallels of latitude at a distance from the equator, north and south, equal to the obliquity of the ecliptic, or 23° 27′, on which the sun is seen in the zenith on the days of its greatest declination: called respectively tropic of Cancer and tropic of Capricorn.
2. Astron. a Either of two corresponding parallels of declination in the celestial sphere similarly named, and respectively 23° 27′ north or south from the celestial equator. b Either of the two points in the celestial sphere where the sun reaches its maximum distance north or south of the celestial equator; a solstice.
3. plural The regions of the earth's surface between the tropics of Cancer and Capricorn, where the sun crosses the zenith twice in the course of the year: with the definite article; the torrid zone.
—adjective Of or pertaining to the tropics; tropical. [<L tropicus <Gk. tropikos (kyklos) the tropical (circle), pertaining to the turning of the sun at the solstice <tropē. See TROPHY.]
TROPICS
a. Tropic of Capricorn.
b. Equator.
c. Tropic of Cancer.

Having a (specified) tropism; turning or changing in a (particular) way, or in response to a (given) stimulus: chemotropic, phototropic.