Definition of envelope in English:

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Pronunciation: /ˈenvəˌlōp/
Pronunciation: /ˈänvəˌlōp/


1A flat paper container with a sealable flap, used to enclose a letter or document.
Example sentences
  • They are all instant communications that are far less bother than putting pen to paper, finding an envelope, licking the flap, sticking on a stamp and popping it in a post box.
  • It is enclosed in a sealed envelope along with this letter.
  • Each letter had a small number in the corner on the backside of the letter; in the envelope was just paper, nothing else.
wrapper, wrapping, sleeve, cover, covering, casing, package
2A covering or containing structure or layer: the external envelope of the swimming pool
More example sentences
  • In summer the fan is reversed, cooling the building by drawing fresh air through louvres in the external envelope.
  • In addition to serving as a semipermeable layer, the envelope in cucumber, muskmelon, and other cucurbitaceous seeds is known to act as the primary barrier to radicle emergence.
  • Construction of the house commenced on-site on October 14 and the structural envelope was erected in an incredible five days.
2.1The outer metal or glass housing of a vacuum tube, electric light, etc.
Example sentences
  • As you know from replacing light bulbs, there is a large, thin, frosted glass envelope in the familiar light bulb shape.
  • The other great problem of glass envelopes is their transparency not only to light, but to much of the electro-magnetic spectrum.
  • The presumption that the glass envelopes of these bulbs function as cutoff filters to remove short wavelength radiation was unsubstantiated.
2.2The structure within a balloon or nonrigid airship containing the gas.
Example sentences
  • They hold open the envelope as the balloon is inflated.
  • At this time of day, the world is wonderfully peaceful - just the sound of distant burners pushing hot air into the envelopes of nearby balloons and songbirds below.
  • He led a team of 12 in Glastonbury, which designed and built the balloon envelope and flight platform.
2.3 Microbiology A membrane forming the outer layer of certain viruses.
Example sentences
  • The insertion of the fusion peptide in the host membrane provides the necessary link between the viral envelope and the cell membrane.
  • The departing viruses therefore have an envelope that can fuse with the membranes of nearby cells, allowing the virus to enter.
  • The cell envelope of gram-positive bacteria consists of the cytoplasmic membrane and a cell wall.
2.4 Electronics A curve joining the successive peaks of a modulated wave.
Example sentences
  • Noise, when used with a vocal modulator, traces the envelope of the vocal with wideband noise.
2.5 Mathematics A curve or surface tangent to each of a family of curves or surfaces.
Example sentences
  • In particular he constructed the tangent plane and exhibited the surface as an envelope of planes.
  • Jacob Bernoulli also discovered a general method to determine evolutes of a curve as the envelope of its circles of curvature.
  • The idea of an envelope of a family of lines had not been mentioned either.
2.6 Astronomy The nebulous covering of the head of a comet; coma.
Example sentences
  • These circumstellar envelopes are indeed progenitors of planetary nebulae.


push the envelope

informal Approach or extend the limits of what is possible: these are extremely witty and clever stories that consistently push the envelope of TV comedy
Originally aviation slang, relating to graphs of aerodynamic performance
More example sentences
  • To say that he bends the rules, pushes the envelope and extends the possibilities of fiction is to state only part of the case.
  • We're trying to push the envelope as much as possible.
  • On more than one occasion, she says, publishers have approached her to push the envelope - to write a novel of her own.


Mid 16th century (in the sense 'wrapper, enveloping layer'): from French enveloppe, from envelopper 'envelop'. The sense 'covering of a letter' dates from the early 18th century.

  • An envelope was originally any kind of wrapper or covering, not just something to put a letter in. It is from the same word as envelop, ‘to wrap up or surround’, from Old French envoluper the en- meaning ‘in’, but the origin of the rest is lost. To push the envelope is to go up to, or beyond, the limits of what is possible, an idea that comes from aeronautics. Since the Second World War the envelope or flight envelope has been the set of combinations of speed, altitude, and range within which a particular kind of aircraft can fly safely. If a test pilot is pushing the envelope he is flying the plane at the very limits of its performance. The phrase came into wider circulation after 1979 following its use in The Right Stuff, a book by American author Tom Wolfe about the early days of the American space programme, later made into an Oscar-winning film.

For editors and proofreaders

Syllabification: en·vel·ope

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