n. 1 a folded paper container, usu. with a sealable flap, for a letter etc. 2 a wrapper or covering. 3 the structure within a balloon or airship containing the gas. 4 the outer metal or glass housing of a vacuum tube, electric light, etc. 5 Electr. a curve joining the successive peaks of a modulated wave. 6 Bot. any enveloping structure esp. the calyx or corolla (or both). 7 Math. a line or curve tangent to each line or curve of a given family.
[ F enveloppe (as ENVELOP) ]