1580s, in torrid zone "region of the earth between the tropics," from Medieval Latin torrida zona, from fem. of torridus "dried with heat, scorching hot," from torrere "to parch," from PIE root *ters- "to dry" (see terrain). Sense of "very hot" is first attested 1610s. Figurative sense from 1630s.[torrid etymology, torrid origin, 英语词源]