In American English, the first syllable is stressed with a short "e" sound, while in British English, the stress is similar, but with a short "o" sound, reflecting a different vowel quality.
The word "envelope" comes from the French word "envelopper," meaning "to wrap, cover, or enclose," which is based on the Old French word "envoluper." The prefix "en-" means "make" or "put in," and "voluper" means "to wrap up." The term entered the English language in the early 18th century. The development of the modern envelope as known today was greatly influenced by the industrial revolution, which allowed for mass production and standardization, making them an integral part of the postal system.