c.1391, "either of the two circles in the celestial sphere which describe the northernmost and southernmost points of the ecliptic," from L.L. tropicus "of or pertaining to the solstice" (as a noun, "one of the tropics"), from L. tropicus "pertaining to a turn," from Gk. tropikos "of or pertaining to
a turn or change, or to the solstice" (as a noun, "the solstice"), from trope "a turning" (see trope
). The notion is of the point at which the sun "turns back" after reaching its northernmost or southernmost point in the sky. Extended 1527 to the corresponding latitudes on the earth's surface (23 degrees 28 minutes north and south); meaning "region between these parallels" is from 1837. Tropical "hot and lush like the climate of the tropics" is first attested 1834.