Real Dictionary

-tropic in American English
turning toward or from, changing because of, or otherwise responding to a (specified kind of) stimulus
combining form: a combining form with the meanings “ turned toward, with an orientation toward” that specified by the initial element (geotropic), “having an affinity for, affecting” what is specified (lipotropic; neurotropic; psychotropic), “affecting the activity of, m

-tropic in British English
combining form in adjective: turning or developing in response to a certain stimulus

tropic in American English
either of two circles of the celestial sphere parallel to the celestial equator, one, the Tropic of Cancer, c. 23° 26 north, and the other, the Tropic of Capricorn, c. 23° 26 south: they are the limits of the apparent north-and-south journey of the sun an
of the tropics; tropical
noun: either of two corresponding parallels of latitude on the terrestrial globe, one (tropic of Cancer) about 231⁄2° N, and the other (tropic of Capricorn) about 231⁄2° S of the equator, being the boundaries of the Torrid Zone

tropic in British English
adjective
noun: either of the parallel lines of latitude at about 231⁄2°N (tropic of Cancer) and 231⁄2°S (tropic of Capricorn) of the equator