In a way relating to existence or being; with respect to existence as the fundamental philosophical concern.
From existential (relating to existence) with the adverbial suffix -ly. The term evolved as philosophy focused more on questions of what it means to exist and to be.
When someone says a problem is 'existentially threatening,' they mean it threatens the very core of who you are or what you believe—it's not just a minor inconvenience, it's a fundamental crisis of meaning!
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