envelope

Etymology 1

From French enveloppe. The engineering sense is derived from flight envelope.

noun

1. A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing.
   Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed envelope, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet. 2013-06-14, Jonathan Freedland, “Obama's once hip brand is now tainted”, in The Guardian Weekly, volume 189, number 1, page 18
2. Something that envelops; a wrapping.
3. A bag containing the lifting gas of a balloon or airship; fabric that encloses the gas-bags of an airship.
   They have no internal or external support structure, being simply a fabric bag (or envelope) filled with a lighter than air gas. Inside the envelope are one or more "ballonets", or smaller bags, which help maintain the envelope's shape. 1992, Lieutenant Colonel Donald E. Ryan, Jr, The airship's potential for intertheater and intratheater airlift, DIANE Publishing, page 46
4. (geometry) A mathematical curve, surface, or higher-dimensional object that is the tangent to a given family of lines, curves, surfaces, or higher-dimensional objects.
5. (electronics) A curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics.
6. (music) The shape of a sound, which may be controlled by a synthesizer or sampler.
7. (computing) The information used for routing a message that is transmitted with the message but not part of its contents.
8. (biology) An enclosing structure or cover, such as a membrane; a space between two membranes
9. (engineering) The set of limitations within which a technological system can perform safely and effectively.
10. (astronomy) The nebulous covering of the head or nucleus of a comet; a coma.
11. An earthwork in the form of a single parapet or a small rampart, sometimes raised in the ditch and sometimes beyond it.
    make a blind all along the bottom of the ditch of the Envelope 1816, James Stanier Clarke, The Life of James the Second King of England

Etymology 2

See envelop.

verb

1. Archaic form of envelop.
   Again, if the plane of the impressed couple intersects the mean plane between N and C, it will envelope the cone whose focals are ON, ON′, and whose internal axis is therefore OA. 1877, James Booth, A Treatise on Some New Geometrical Methods, page 209