envelope

/ˈenvələʊp/ (bre, ipa) · /ˈenvələʊp/ (ame, ipa) · /ˈen-və-ˌlōp ˈän-/ (ame, mw)

envelope — noun

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

1.名詞A2
釋義

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

例句

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.

同義詞
  • 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

用法筆記

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.

常見錯誤

❌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.名詞B2
釋義

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.

例句

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.

同義詞
  • 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

文法句型

envelope + of + [noun]

用法筆記

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.名詞C1
釋義

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

例句

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

同義詞
  • 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

文法句型

flight envelope

cost envelope

push the envelope

用法筆記

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.'

常見錯誤

❌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.