# envelope

Pronunciation: say "EN-vuh-lohp" US /ˈɛnvəˌloʊp/, UK /ˈɛnvələʊp/

## Noun

1. A flat paper or cardboard wrapper that encloses letters or other small, flat items for mailing.
   - Simple: A flat paper cover that holds a letter or card for mailing.
   - _The clerk weighed each envelope before applying the correct postage._
   - _A stack of unopened envelopes sat on the corner of the desk._
2. A covering or wrapping that encloses something.
   - Simple: A covering or layer that wraps around something.
   - _A warm envelope of air surrounded the plants in the greenhouse._
   - _Clouds formed a gray envelope around the mountain peak._
3. The range of limits within which a technological system can operate safely and effectively.
   - Simple: The safe limits that a machine or system must stay inside to work well.
   - _Engineers map the flight envelope before clearing the jet for service._
   - _Operating beyond the design envelope risks sudden structural failure._
4. A covering that encloses a structure, such as the membrane around a cell nucleus or a virus, or the space between two such membranes.
   - Simple: A covering layer, such as a membrane, that surrounds part of a cell.
   - _The nuclear envelope separates the chromosomes from the rest of the cell._
   - _Some viruses shed their lipid envelope as they enter a host cell._
5. The fabric bag that contains the lifting gas of a balloon or airship, or the covering that encloses an airship's gas-bags.
   - Simple: The large fabric bag that holds the gas which lifts a balloon or airship.
   - _Ground crew unfurled the vast envelope across the field before inflation._
   - _A small tear in the envelope forced the airship to land early._
6. The profile of a sound over time, such as how its loudness rises and falls, which a synthesizer or sampler can be set to shape.
   - Simple: The way a sound's loudness changes over time, from start to finish.
   - _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._
7. The routing information transmitted along with a message but kept separate from its contents.
   - Simple: The address details sent with a message to help it reach the right place, kept apart from the message itself.
   - _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._
8. A curve, surface, or higher-dimensional object that is tangent to every member of a given family of such objects.
   - Simple: A curve or surface that just touches every curve in a related group.
   - _The envelope of a family of straight lines can form a smooth curve._
   - _Students computed the envelope traced by a moving tangent line._
9. A 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.
   - Simple: A smooth curve that outlines the peaks of a changing signal.
   - _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._
10. The hazy cloud of gas and dust that surrounds the head or nucleus of a comet.
   - Simple: A faint, cloudy layer surrounding the head 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._
11. An earthwork in the form of a single parapet or small rampart, sometimes raised within the ditch and sometimes beyond it.
   - Simple: A low bank of earth built as a defense, sometimes inside a 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._

## Verb

12. To place something inside an envelope. *(rare)*
   - Simple: To put something inside a paper cover for mailing.
   - _The clerk will envelope each statement before mailing it._
   - _She enveloped the photographs and addressed them to her sister._
13. Archaic form of envelop. *(archaic)* — Archaic form of envelop. (pronounced: say "en-VEL-uhp" /ɛnˈvɛləp/)
   - Simple: Archaic form of envelop. An old spelling meaning to wrap or surround something completely.

## Origin

This word comes from the French "enveloppe." The engineering sense comes from "flight envelope," and the verb comes from the noun.

Source: DictionaryAI, https://dictionaryai.com/define/envelope (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).