Tropic
late Middle English (denoting the point on the ecliptic reached by the sun at the solstice): via Latin from Greek tropikos, from tropē ‘turning’, from trepein ‘to turn’.
wiktionary
From Late Latin tropicus(“of or pertaining to the solstice, as a noun, one of the tropics”), from Ancient Greek τροπικός(tropikós, “of or pertaining to a turn or change; or the solstice; or a trope or figure; tropic; tropical; etc.”), from τροπή(tropḗ, “turn; solstice; trope”).
etymonline
tropic (n.)
late 14c., "either of the two circles in the celestial sphere which describe the northernmost and southernmost points of the ecliptic," from Late Latin tropicus "of or pertaining to the solstice" (as a noun, "one of the tropics"), from Latin tropicus "pertaining to a turn," from Greek tropikos "of or pertaining to a turn or change; of or pertaining to the solstice" (as a noun, "the solstice," short for tropikos kyklos), from trope "a turning" (from PIE root *trep- "to turn").
The notion is of the point at which the sun "turns back" after reaching its northernmost or southernmost point in the sky. Extended 1520s to the corresponding latitudes on the earth's surface (23 degrees 28 minutes north and south); meaning "region between the tropics of Cancer and Capricorn" is from 1837.
