envelope
Pluralenvelopes
Pluralenvelopes
Formsenvelopes, enveloping, enveloped
- 1A flat paper or cardboard wrapper that encloses letters or other small, flat items for mailing.
The clerk weighed each envelope before applying the correct postage.
A stack of unopened envelopes sat on the corner of the desk.
Note
The everyday sense, and the one the word's French origin points to: English took it from enveloppe, and the mailing verb was made from this noun. A sealed envelope is the classic picture of a private message. Jonathan Freedland, writing in The Guardian in 2013, sets the sealed love letter against the secrets people now spray into the public ether.
- 2A covering or wrapping that encloses something.
A warm envelope of air surrounded the plants in the greenhouse.
Clouds formed a gray envelope around the mountain peak.
Similarwrapper
- 3The range of limits within which a technological system can operate safely and effectively.
Like a fenced playing field: everything works inside the boundaries, but cross them and the game breaks down.
Engineers map the flight envelope before clearing the jet for service.
Operating beyond the design envelope risks sudden structural failure.
Note
The engineer's sense comes from aviation's flight envelope, the boundary of speeds, loads and altitudes a craft can safely handle. Its best-known idiom is push the envelope, meaning to work at or just past those limits. Tom Wolfe's The Right Stuff (1980) uses the picture spatially: the test pilots knew where the outside of the envelope was.
- 4A covering that encloses a structure, such as the membrane around a cell nucleus or a virus, or the space between two such membranes.
The nuclear envelope separates the chromosomes from the rest of the cell.
Some viruses shed their lipid envelope as they enter a host cell.
Similarmembrane
Note
Biologists use the word for coverings built from membranes, and it appears mostly in fixed pairings: the nuclear envelope around a cell's chromosomes, the lipid envelope of certain viruses. The nuclear envelope is a double membrane. That explains the less obvious half of the sense, in which envelope can name the thin space between two membranes as well as the cover itself.
- 5The fabric bag that contains the lifting gas of a balloon or airship, or the covering that encloses an airship's gas-bags.
Ground crew unfurled the vast envelope across the field before inflation.
A small tear in the envelope forced the airship to land early.
Similargasbag
Note
Two structures share the name, depending on the craft. In a simple balloon the envelope is the gasbag itself. In an airship with separate gas-bags inside, it is the outer fabric enclosing them. Lieutenant Colonel Donald E. Ryan, Jr, writing on airships in 1992, describes smaller bags called ballonets that sit inside the envelope and help it keep its shape. Gasbag is the plainer synonym.
- 6The profile of a sound over time, such as how its loudness rises and falls, which a synthesizer or sampler can be set to shape.
Producers shape the volume envelope to control how quickly each note swells and fades.
Tweaking the filter envelope made the synth line grow brighter over time.
Note
Synthesists treat a sound as having a shape in time, and the envelope is the control that sets it. The classic contour runs through attack, decay, sustain and release. These stages govern how fast a note swells, how it settles and how it dies away. The word usually comes with what it shapes: a volume envelope, a filter envelope, an amplitude envelope.
- 7The routing information transmitted along with a message but kept separate from its contents.
The email's envelope tells the server who should receive it, even when the header says otherwise.
Spam filters often inspect the envelope before the message body is examined.
Similarheader
Note
The postal picture carried into networking. Like the address written on the outside of a paper envelope, this information tells the system where a message goes without being part of what it says. Sender, recipient and handling instructions travel here, while the body stays sealed inside. Header is offered as a near synonym.
- 8A curve, surface, or higher-dimensional object that is tangent to every member of a given family of such objects.
The envelope of a family of straight lines can form a smooth curve.
Students computed the envelope traced by a moving tangent line.
Note
Geometry speaks of the envelope of a family. Draw many straight lines, each shifted slightly from the last, and the curve they all touch emerges as their envelope, outlined by lines that never draw it directly. Each member meets the envelope at a point of tangency. In use the word almost always takes of followed by the family it belongs to.
- 9A curve that marks the outer limit of another curve or group of curves, for example the outline traced by the peaks of an amplitude-modulated carrier wave.
An AM receiver extracts the audio by following the envelope of the carrier wave.
The oscilloscope display showed the envelope rising and falling with the signal.
Note
Close kin to the tangent-curve meaning, but here the curve bounds a rapidly varying wave instead of touching a family of curves. In an amplitude-modulated signal, the envelope traces the peaks of the carrier. The envelope, not the carrier itself, carries the transmitted information, which is why a receiver follows its rise and fall.
- 10The hazy cloud of gas and dust that surrounds the head or nucleus of a comet.
Astronomers measured the envelope of gas and dust spreading from the comet's core.
As the comet warmed, its envelope expanded into a glowing halo.
Similarcoma
Note
Astronomy's envelope is the hazy cloud of gas and dust surrounding a comet's nucleus. It forms as the Sun warms the nucleus, turning its ices to gas and releasing dust, and it swells as the comet heats. Coma names the same cloud, and either word can be used for it.
- 11An earthwork in the form of a single parapet or small rampart, sometimes raised within the ditch and sometimes beyond it.
Engineers threw up an envelope along the ditch to shield the main rampart.
Attackers had to cross the envelope before reaching the fortress wall.
Note
A term of fortification for an outer line of earth thrown up to give a defense an extra parapet, either inside the ditch or beyond it. James Stanier Clarke's Life of James the Second (1816) treats it as a named part of the works, capitalizing it: "the ditch of the Envelope."
Less common meanings
- 12To place something inside an envelope.
The clerk will envelope each statement before mailing it.
I suspect you write letters as hens lay eggs, find that Lady Hamilton finds them, envelopes them, puts them before you as official letters, and you direct them as per memorandum affixed.
1857, Augustus de Morgan, “[Correspondence between Sir William Rowan Hamilton and Professor Augustus De Morgan.] From A. De Morgan to Sir…Note
A rare verb made from the paper envelope, at home in clerical and letter-writing settings. Louis Bagger's 1873 account of the Dead-Letter Office has clerks reënveloping returned letters. In William De Morgan's The Old Madhouse (1919), a man re-enveloped and pocketed a letter. Its forms enveloped and enveloping are spelled exactly like those of envelop, so only context shows that a letter is meant.
- 13Sayen-VEL-uhp/ɛnˈvɛləp/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 MethodsNote
An older spelling of envelop, the verb meaning to surround or enfold. In current writing, envelop is the form to use. Mathematical prose kept the old spelling: James Booth's Treatise on Some New Geometrical Methods (1877) writes that a plane "will envelope the cone," a usage close in spirit to the tangent-curve meaning.
Showing meanings only.
Practice
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Origin
This word comes from the French "enveloppe." The engineering sense comes from "flight envelope," and the verb comes from the noun.