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English definition of “acid test”

acid test

noun [C usually sing]  /ˈæs·ɪd ˈtest/
the proof of the value of something, or the standard that something must meet in order to prove its value: In 1933, the pressurized airplane passed the acid test when it flew from Chicago to Washington at 22,000 feet above heavy storm clouds.
(Definition of acid test noun from the Cambridge Academic Content Dictionary © Cambridge University Press)

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