envelope

American  

[en-vuh-lohp, ahn-] / ˈɛn vəˌloʊp, ˈɑn- /

noun

1. a flat paper container, as for a letter or thin package, usually having a gummed flap or other means of closure.

2. something that envelops; a wrapper, integument, or surrounding cover.

3. Biology. a surrounding or enclosing structure, as a corolla or an outer membrane.

4. Geometry. a curve or surface tangent to each member of a set of curves or surfaces.

5. Radio. (of a modulated carrier wave) a curve connecting the peaks of a graph of the instantaneous value of the electric or magnetic component of the carrier wave as a function of time.

6. the fabric structure enclosing the gasbag of an aerostat.

7. the gasbag itself.

8. Electronics. the airtight glass or metal housing of a vacuum tube.

9. the technical limits within which an aircraft or electronic system may be safely operated.

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idioms

1. push the envelope, to stretch established limits, as in technological advance or social innovation.

envelope British  

/ ˈɒn-, ˈɛnvəˌləʊp /

noun

1. a flat covering of paper, usually rectangular in shape and with a flap that can be folded over and sealed, used to enclose a letter, etc

2. any covering or wrapper

3. biology any enclosing structure, such as a membrane, shell, or skin

4. the bag enclosing the gas in a balloon

5. maths a curve or surface that is tangent to each one of a group of curves or surfaces

6. electronics the sealed glass or metal housing of a valve, electric light, etc

7. telecomm the outer shape of a modulated wave, formed by the peaks of successive cycles of the carrier wave

8. informal to push the boundaries of what is possible

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Etymology

Origin of envelope

1700–10; < French enveloppe, derivative of envelopper to envelop

Explanation

An envelope is something that envelops, or wraps around. It usually refers to the thing you stick a stamp on and snail mail. In the early 1700s, envelope, the noun for "wrapper," evolved from the French enveloppe, meaning “to envelop.” Envelope is always a noun, unlike the verb envelop which means “to wrap, cloak.” Synonyms for envelope range from casing and enclosure to pouch and sheath. Virginia Woolf said, “Life is a luminous halo, a semi-transparent envelope surrounding us from the beginning.” She ditched hers by walking into a river with her pockets full of rocks.

Example Sentences

But as much as he enjoyed pushing the envelope on the track, one of his greatest passions was taking his retrofitted classic cars on leisurely drives in the Santa Monica Mountains.

From Los Angeles Times • Apr. 9, 2026

Make sure to see the envelope handstamped with the postmark instead of tossing the letter in the mailbox, O’Saben added.

From MarketWatch • Apr. 9, 2026

The envelope contained £100 in £20 notes, and was signed: "A former foolish student."

From BBC • Mar. 24, 2026

Samples exposed to 2.4 GPa began to show ruptured membranes, but the structure of the bacterium’s cell envelope help explain the survival of 60% of microbes.

From Science Daily • Mar. 3, 2026

Lying on the floor near the door is an envelope.

From "The Bletchley Riddle" by Ruta Sepetys and Steve Sheinkin

Related Words

• bag
• box
• casing
• coat
• container
• jacket
• pocket
• pouch