- noun a difficult or exacting test of worth or quality
- noun a party or informal ritual at which a group of people take food and/or drink laced with LSD. The expression and the practice were originated by Ken Kesey and the Merry Pranksters, a group of hedonistic travellers in the USA in the early 1960s who were successors to the beats and precursors of the hippies.
Idiom of “acid test”
method of proving the worth, truth, etc. of something