noun
a flat (usually rectangular) container for a letter, thin package, etc.
noun
any wrapper or covering
noun
a curve that is tangent to each of a family of curves
noun
a natural covering (as by a fluid)
Examples
- the spacecraft detected an envelope of gas around the comet
noun
the maximum operating capability of a system (especially an aircraft)
Examples
- test pilots try to push the envelope
noun
the bag containing the gas in a balloon
Synonyms