noun.
A device which automatically regulates temperature, or provides a signal used by another device to regulate temperature. The temperature-sensitive signal may be electronic, as that produced by a thermocouple. The signal may also be caused mechanically, as by the unequal expansion of different metals, liquids, or gases by heat, which can then cause the opening or closing of the damper of a stove, or the like, as the heat becomes greater or less than is desired.