A violent release of energy caused by a chemical or nuclear reaction WordNet 3.0 & Open English WordNet

An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Wikipedia

Sudden increase in volume and release of energy in an extreme manner. Wikipedia Disambiguation

A violent, sudden release of energy resulting from powders or gases undergoing instantaneous ignition or from some other means of detonation, often accompanied by a force producing great amounts of heat, major structural damages, shock waves and flying shrapnel. OmegaWiki

A violent release of energy (sometimes mechanical, nuclear, or chemical.). Wiktionary

Violent release of energy. Wiktionary (translation)