- a unit of one million deaths: used in estimating or predicting the fatalities that would occur in a nuclear war.
- the death of a million people, esp in a nuclear war or attack
n.1953, from mega- in scientific sense (one million) + death (n.). The death of one million persons, as a measure of the effectiveness of nuclear weapons. The resulting pile of dead bodies would be a megacorpse, according to writings on the topic.