That omits entirely the origin and meaning of the word proof in this context. Proof originally related to proving that the alcohol content was of such a degree

That omits entirely the origin and meaning of the word proof in this context. Proof originally related to proving that the alcohol content was of such a degree that excise duty was due not to actually measuring the alcohol content. "In 16th-century England, the original test involved soaking a pellet of gunpowder with the liquor. If it was still possible to ignite the wet gunpowder, the alcohol content of the liquor was rated above proof and it was taxed at a higher rate, and vice versa if the powder failed to ignite." https://homepages.uc.edu/~jensenwb/reprints/111.%20Proof.pdf https://homepages.uc.edu/~jensenwb/reprints/111.%20Proof.pdf