Definition of envelope in English:


Syllabification: en·vel·ope
Pronunciation: /ˈenvəˌlōp
, ˈänvəˌlōp


1A flat paper container with a sealable flap, used to enclose a letter or document.
More 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.
More 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.
More 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.
More 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.
More 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.
More 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.
More example sentences
  • These circumstellar envelopes are indeed progenitors of planetary nebulae.


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.


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.

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Word of the day retroflex
Pronunciation: ˈretrəˌfleks
turned backward