Therm words therm a unit of heat that equals 1000 great calories thermal related to heat or temperature endothermic heated from within the body exothermic requires heat to be absorbed from outside the body thermos a container used to keep things warm thermometer a device used to measure temperature thermostat a device used to adjust the temperature in a room thermopile an organism that has adapted to living in very high temperatures thermodynamic caused or operated by heat that has changed into different forms of energy thermograph keeping a record of different temperatures changes