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