Tropic of Cancern. The parallel of latitude 23°26? north of the equator, the northern boundary of the Torrid Zone, and the most northerly latitude at which the sun can shine directly overhead.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.trop?ic (?tr?p ?k) n. 1. a. either of two corresponding parallels of latitude on the terrestrial globe, one (tropic of Cancer) about 23½° N, and the other (tropic of Capricorn) about 23½° S of the equator, being the boundaries of the Torrid Zone. b. the tropics, the regions lying between and near these parallels of latitude; the Torrid Zone and neighboring regions. 2. either of two circles on the celestial sphere, one lying in the same plane as the tropic of Cancer, the other in the same plane as the tropic of Capricorn. adj. 3. of or pertaining to the tropics; tropical. [1350?1400; Middle English