From French enveloppe 'wrapper,' from envelopper 'to wrap up' — etymologically the opposite of 'develop.'
A flat paper container with a sealable flap, used for enclosing a letter.
From French enveloppe, from envelopper 'to wrap up,' from en- 'in' + a second element of uncertain origin (possibly Frankish *wlapan or Celtic *vol- 'to roll'). The word arrived in English as a military term for a defensive earthwork before gaining its postal sense. Key roots: en- + *wlapan (uncertain) (French/Frankish: "to wrap in").