noun

1. Astron. 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 and are determined by the obliquity of the ecliptic
2. Geog. either of two parallels of latitude (Tropic of Cancer
   and Tropic of Capricorn

   ) situated on either side of the earth's equator that correspond to the astronomical tropics

Etymology: ME tropik < LL tropicus < Gr tropikos, belonging to a turn (of the sun at the solstices) < tropē: see trope

adjective