envelope

noun

1. a flat (usually rectangular) container for a letter, thin package, etc.

   Less specific

   • container

   More specific

   • window envelope

2. any wrapper or covering

   Less specific

   • wrapping, wrap, wrapper

3. a curve that is tangent to each of a family of curves

   Less specific

   • curve, curved shape

4. a natural covering (as by a fluid); “the spacecraft detected an envelope of gas around the comet”

   Less specific

   • covering, natural covering, cover

5. the maximum operating capability of a system (especially an aircraft); “test pilots try to push the envelope”

   Less specific

   • operating capability, performance capability

6. the bag containing the gas in a balloon

   Synonyms

   • gasbag

   Less specific

   • bag

   Part of

   • balloon