exothermic

adj. emitting heat

In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. Its etymology stems from the Greek prefix ex-, meaning “outside” and the Greek word thermein, meaning “to heat”. The opposite of an exothermic process is an endothermic process, one that absorbs energy in the form of heat. The term “exothermic” was coined by Marcellin Berthelot.
See more at Wikipedia.org...

Compare with endothermic .An exothermic process is a process that releases heat. A negative sign on heat or on the enthalpy change associated with a process indicates that it is exothermic.

Adjective
1. (of a chemical reaction or compound) occurring or formed with evolution of heat
(synonym) exothermal, heat-releasing
(antonym) endothermic, endothermal, heat-absorbing
(see-also) exoergic, energy-releasing