What is the meaning of Tropic?

Either of the two parallels of latitude 23°27′ north and south of the equator; the farthest points at which the sun can be directly overhead; the boundaries of the torrid zone or tropics.

Of, or relating to the tropics; tropical.

Hot and humid.

Having the quality of indirectly inducing a biological or chemical change in a system or substrate.

Pertaining to, involving, or of the nature of a trope or tropes.

tropic

Source: wiktionary.org