Following the Brussels attack, President Obama made a statement that sent many people scrambling for their dictionaries:
Groups like ISIL can’t destroy us, they can’t defeat us. They don’t produce anything. They’re not an existential threat to us. They are vicious killers and murderers who perverted one of the world’s great religions.
Existential means “of, relating to, or affirming existence”; an existential threat is a threat to the existence of something. In this case, President Obama was referring to the potential destruction of the United States. “Existential threat” is a term that gained currency during the cold war, when the Soviet nuclear threat scared the public and determined policy. Unsurprisingly, the use of “existential threat” increased in the mid-80s, during the final years of the Soviet Union. It is now used more frequently than ever.
Some critics of the president mocked his use of the term existential because it also refers to the philosophical school of existentialism, but that meaning is very specific to its academic field.