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Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: An SI unit of time equal to 10²⁴ seconds. Symbol: Ys. (= quadrillions of years, a hypothetical time span that is meaningless except in speculative contexts such as theoretical physics, philosophy, religion, and humorous hyperbole) Full definition →
Etymology from Wiktionary, CC BY-SA 4.0.