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Related to acid test: Acid Test Ratio
A conclusive test. The phrase comes from the 19th-century practice of testing metals in nitric acid to determine if they contained gold. Restructuring the organization will be the acid test that determines whether or not it can survive the sudden downturn in the economy.
Fig. a test whose findings are beyond doubt or dispute. The senator doesn't look too popular just now, but the acid test will be if he gets reelected.
A decisive trial to determine worth or quality, as in Exposure to brilliant sunlight is the acid test for showing this fabric won't fade. Alluding to a 19th-century chemical test for distinguishing gold from other metals, this term was used figuratively by the early 1900s.
the acid test
COMMON If you call something the acid test, it will prove how effective or useful something is. The acid test for the vaccine will be its performance in the south where the disease is more widespread. So far, I don't feel too bad but I'm waiting for my first really stressful day when things go wrong. That will be the real acid test. Note: Nitric acid can be used to test whether a metal is pure gold because it damages most metals but does not affect gold.
the acid testa situation or event which finally proves whether something is good or bad, true or false, etc.
The original use of the phrase was to describe a method of testing for gold with nitric acid (gold being resistant to the effects of nitric acid).
1990 Which? These deals are designed to encourage impulse buying, so the acid test is whether you would have bought anyway.