the word 'waterproof' is a transparent compound formed within english from the native germanic noun 'water' and the suffix 'proof', which entered english via french and latin. the logic is direct and utilitarian: something that is 'proof' against water. the suffix 'proof' evolved from the latin concept of testing ('probare') to the middle english sense of proving something's strength, and finally to its modern combinatory meaning of providing protection or resistance. thus, the term literally means 'resistant to the test of water,' a meaning that has remained consistent since its formation in the early 19th century.

Structure: water (liquid) + proof (resistant) water: from old english 'wæter', of germanic origin; related to dutch 'water' and german 'wasser', from an indo-european root shared by sanskrit 'udan', greek 'hydōr', and latin 'unda' (wave). functions as the base noun denoting the substance. proof: from old french 'prove', from late latin 'proba', from latin 'probare' meaning 'to test, prove'. the sense 'resistant' (as in 'fireproof') developed from the idea of being able to withstand a test or assault. functions as a combining form meaning 'impervious to, resistant to'.