envelope

envelope — noun

1. A folded paper case with a gummed flap, used to hold and protect a letter for se

1.nounA2
Definition

A folded paper case with a gummed flap, used to hold and protect a letter for sending through the mail.

Example

Feng sealed the envelope before walking to the post office.

collocation: seal an envelope

A thick cream-colored envelope sat on the kitchen table with no stamp on it.

Common collocations
  • seal an envelope
  • open an envelope
  • address an envelope
  • stamp an envelope
  • envelope flap
  • #10 envelope
Synonyms
  • packet

    a small container or package, often but not always for letters

  • mailer

    a padded envelope used for shipping, more specific

  • wrapper

    a paper covering, not necessarily designed for mailing

Usage Note

The related verb 'envelop' (no final 'e') means 'to cover or surround completely' and is pronounced differently (en-VEL-up). Learners often misspell one for the other.

Common Mistakes

Please envelope the gift in wrapping paper.
Please envelop the gift in wrapping paper.
'Envelop' is the verb; 'envelope' is the noun.
I put the letter in an envelop.
I put the letter in an envelope.
The noun requires the final 'e'.

2. A layer of material that fully surrounds and encloses an object, for example a c

2.nounB2
Definition

A layer of material that fully surrounds and encloses an object, for example a cell's outer membrane, a planet's atmosphere, or a plastic coating.

Example

The cell membrane forms a thin protective envelope around every living cell.

scientific context: membrane as envelope

Vikram studied the gas envelope that surrounds the planet Venus.

Common collocations
  • gas envelope
  • cell envelope
  • protective envelope
  • envelope of gas
  • outer envelope
Synonyms
  • covering

    more general; any layer that covers something

  • membrane

    specifically a thin biological or synthetic film, not a general wrapper

  • sheath

    a close-fitting protective covering, often for a blade or cable

Grammar Patterns

envelope + of + [noun]

Usage Note

Common in biology (cell envelope), astronomy (gas envelope), and engineering (protective envelope). In everyday speech, 'covering' or 'wrapper' is preferred.

3. The set of conditions or performance boundaries within which a machine, system,

3.nounC1
Definition

The set of conditions or performance boundaries within which a machine, system, or project can operate safely or effectively.

Example

The test pilot pushed the aircraft's flight envelope to its absolute limit during the trial.

collocation: flight envelope

Every new engineering project must operate within a defined cost envelope.

collocation: cost envelope

Common collocations
  • flight envelope
  • safety envelope
  • cost envelope
  • performance envelope
  • push the envelope
Synonyms
  • limit

    more general; a point beyond which something cannot go

  • boundary

    a dividing line; more spatial than 'limit'

  • parameter

    a measurable factor that defines a system; more technical

Grammar Patterns

flight envelope

cost envelope

push the envelope

Usage Note

Originally an aviation term for an aircraft's speed-and-altitude safe-operating region. The phrase 'push the envelope' (see idiom below) has extended into general use to mean 'go beyond conventional limits.'

Common Mistakes

We need to push the envelope of our marketing strategy.' (vague)
We need to push the envelope by trying new advertising channels.
Add concrete detail about what boundary is being crossed.
Idioms

push the envelope

idiom

To go beyond the usual or accepted limits of what is considered possible, acceptable, or safe in a particular area.

The fashion designer pushed the envelope with bold colors and unusual fabric combinations.

Tunde's startup pushed the envelope by using AI to solve a problem nobody had tackled before.

back-of-the-envelope

idiom

Describing a calculation, estimate, or plan that is done quickly and roughly, without detailed analysis or precise data.

We did a back-of-the-envelope estimate and found the project would cost around fifty thousand dollars.

A back-of-the-envelope calculation suggested the trip would take about three hours by car.

(on the) back of an envelope

idiom

Done in a quick and simple way, without exact details.

Maya did a back-of-the-envelope estimate for the project cost.

Can you calculate the budget on the back of an envelope?

Word family

  • envelop
    verbB2
  • enveloping
    adjectiveC1
  • envelopment
    nounC2

Synonym discussion

Sense: noun/1

'Envelope' refers specifically to a flat paper container with a sealable flap, designed for mailing letters. A 'packet' is a small container or package that may hold documents or small objects; it is often sturdier than an envelope and not necessarily sealable by licking a flap. A 'folder' is a folded card or flexible cover for storing loose papers, typically without adhesive closure. A 'wrapper' is any paper or material that covers an object but lacks the letter-sized shape and mailing features of an envelope. For example, you mail a letter inside an envelope, file papers in a folder, receive small goods in a packet, and peel the wrapper off a candy bar.

envelope ↗packet ↗folderwrapper

Common collocations

Phrases

  • seal the envelope
  • open the envelope
  • address the envelope
  • push the envelope
  • flight envelope
  • cost envelope

Prepositions

  • inside an envelope
  • within an envelope
  • outside an envelope

Etymology

FrenchEnglish

Borrowed from French 'enveloppe', from Old French 'envoluper' meaning 'to wrap up' or 'to envelop'. The noun entered English in the early 1700s, first referring to the paper container for letters. The verb 'envelop' (without final 'e') entered English earlier, in the 1300s. The figurative use of 'envelope' for performance limits dates from the mid-20th century, popularised in aviation.