Noun

(en noun)

A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing.

* {{quote-magazine, date=2013-06-14, author=(Jonathan Freedland)

, volume=189, issue=1, page=18, magazine=(The Guardian Weekly) , title= Obama's once hip brand is now tainted , passage=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.}}

Something that envelops; a wrapping.

A bag containing the lifting gas of a balloon or airship; fabric that encloses the gas-bags of an airship.

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(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.

(electronics) A curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics.

(music) The shape of a sound, which may be controlled by a synthesizer or sampler.

(computing) The information used for routing an email that is transmitted with the email but not part of its contents.

(biology) An enclosing structure or cover, such as a membrane.

(engineering) The set of limitations within which a technological system can perform safely and effectively.

(astronomy) The nebulous covering of the head or nucleus of a comet; a coma.

An earthwork in the form of a single parapet or a small rampart, sometimes raised in the ditch and sometimes beyond it.

(Wilhelm)