1.Definition: a curve that is tangent to each of a family of curves

Category: General

2.Definition: a flat (usually rectangular) container for a letter, thin package, etc.

Category: Objects

3.Definition: a natural covering (as by a fluid)

"The spacecraft detected an envelope of gas around the comet"

Category: Objects

4.Definition: any wrapper or covering

Category: Objects

5.Definition: the bag containing the gas in a balloon

Related Noun(s):gasbag

Category: Objects

6.Definition: the maximum operating capability of a system (especially an aircraft)

"Test pilots try to push the envelope"

Category: General