Definition of envelope in English:

envelope

Line breaks: en¦ve|lope
Pronunciation: /ˈɛnvələʊp
 
, ˈɒn-/

noun

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.
Synonyms
wrapper, wrapping, wrap, sleeve, cover, covering;
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. the switch itself is a glass envelope filled with rare gases and containing two contacts
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 non-rigid 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 which forms 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.

Origin

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

Phrases

the back of an envelope

Used in reference to calculations or plans of the most sketchy kind: a proposal drawn up on the back of an envelope
More example sentences
  • The Scottish Socialist Party wants to get rid of the council tax and have done some calculations on the back of an envelope in order to redistribute the burden of local taxation.
  • It's much higher than the age pension, but a quick calculation on the back of an envelope will tell you that it's not going to allow many of the activities we might hope for in retirement - travel, entertainment, books and the like.
  • Simple calculations on the back of an envelope will do for a start.

push the envelope (or the edge of the envelope)

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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