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| en·ve·lope [ énvə lp, ónvə lp ] (plural en·ve·lopes) |
noun |
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| Definition: |
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1. paper cover for letter: a flat pocket of paper with a sealable flap for holding a letter
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2. enclosing case: something that surrounds or encloses something else
  seafood sauce in phyllo pastry envelopes
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3. zoology enclosing structure: a covering that encloses and protects an animal's body or a biological structure, e.g. a shell or membrane
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4. mathematics curve forming tangent: a curve or surface that forms a tangent to each of the members of a set of curves or surfaces, e.g. circles with a common center but different radii
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5. aviation balloon: the bag of an airship or balloon that contains the gas
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6. aviation performance limits of aircraft: the performance limits of a piece of equipment, particularly of an aircraft
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| [Early 18th century. < French enveloppe< envelopper "wrap in"] |
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push the envelope to try to accomplish more than is theoretically possible (informal)
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