The word "weatherproof" is a transparent compound formed within Modern English. Its first element, "weather," descends from the Proto-Germanic wedrą, which carried the sense of storm or wind, reflecting the primary environmental force to be guarded against. The second element, "proof," entered English via Old French from the Latin verb probare (to test or prove), evolving to denote something that has been tested and found resistant. The compound's logic is direct and functional: it describes an object that has been made resistant to the test posed by harsh weather conditions, shifting the sense of "proof" from abstract validation to a concrete, protective quality.

Structure: weather (weather) + proof (resistant) - weather: From Old English weder, meaning "air, sky, breeze, storm, weather." Its functional role is the core noun denoting atmospheric conditions. - proof: From Old French preuve, meaning "evidence, test," and ultimately from Latin probare ("to test, prove"). Its functional role is a suffix meaning "impervious to, resistant to, able to withstand."