Origins
The paper envelope is surprisingly modern.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ People sent sealed letters for centuries using wax, ribbon, or folded paper, but the separate enclosing sleeve β the envelope β only became standard in the early 19th century, after mechanised paper-making brought costs down.
The word arrived in English from French enveloppe, the noun form of envelopper ('to wrap up'), from Old French envoluper. The deeper origin is uncertain. Most scholars connect voloper to a pre-Romance or Celtic root meaning 'to wrap', though some link it to Latin volvere ('to roll').
French Influence
The most striking relationship is with develop. Old French desveloper (later dΓ©velopper) meant 'to unwrap' β the prefix des- reversing the wrapping action of en-. To develop something was to expose what had been covered. Photography preserved this sense perfectly: developing a photograph meant revealing the latent image wrapped in the emulsion.
The phrase 'pushing the envelope' comes from aviation, not stationery. The flight envelope is the set of conditions under which an aircraft can safely operate β a mathematical boundary that wraps around all possible speeds, altitudes, and angles. Test pilots who pushed it were testing the outer limits of the wrapping.