- a flat paper container with a sealable flap, used to enclose a letter or document.；a covering or containing structure or layer
noun: envelope, plural noun: envelopes
- 1. a flat paper container with a sealable flap, used to enclose a letter or document.
- 2. a covering or containing structure or layer the external envelope of the swimming pool
- ▪ the outer metal or glass housing of a vacuum tube, electric light, etc. the switch itself is a glass envelope filled with rare gases and containing two contacts
- ▪ the structure within a balloon or non-rigid airship containing the gas.
- ▪ a membrane which forms the outer layer of certain viruses.
- ▪ a curve joining the successive peaks of a modulated wave.
- ▪ a curve or surface tangent to each of a family of curves or surfaces.