Thermostat: A device that monitors temperature and automatically maintains it at certain levels. In a human, a tiny part of the brain called the hypothalamus, located behind the eyes, serves as the thermostat. It can warm the body by causing it to shiver and cool the body by causing it to perspire. The hypothalamus also regulates hunger, thirst, sex drive and other body activities.
"Thermostat" is derived from the Greek "therme" (heat) and "statos" (standing, stationary). Other words formed from "therme" include "thermometer" (a device for measuring temperature) and "thermotherapy" (the use of heat to treat disease).