Calorimeter

Calorimeter is an apparatus for measuring quantities of absorbed or emitted heat or for determining specific heats.

A calorimeter is a device used to measure the heat flow of a chemical reaction or physical change. The process of measuring this heat is called calorimetry. A basic calorimeter consists of a metal container of water above a combustion chamber, in which a thermometer is used to measure the change in water temperature. However, there are many types of more complex calorimeters.
The basic principle is that heat released by the combustion chamber increases the temperature of the water in a measurable way. The temperature change may then be used to calculate the enthalpy change per mole of substance A when substances A and B are reacted.
The equation used is:
q = Cv(Tf - Ti )
where:
q is the amount of heat in joules
Cv is the calorimeter's heat capacity in joules per Kelvin (J/K)
Tf and Ti are the final and initial temperatures.

Sources:

Словник Webster's Dictionary https://www.merriam-webster.com/

ThoughtCo. Dictionary https://www.thoughtco.com/definition