- The definition of exothermic is a process or chemical reaction characterized by or causing the liberation or release of heat.
Combustion where heat is released is an example of an exothermic reaction.
designating or of a chemical change in which there is a liberation of heat, as in combustion
Origin of exothermicexo- + thermic
Releasing heat: an exothermic reaction.
(comparative more exothermic, superlative most exothermic)