📖 WordNook

envelope

noun
  1. any wrapper or covering
  2. a flat (usually rectangular) container for a letter, thin package, etc.
  3. the bag containing the gas in a balloon
    gasbag
  4. the maximum operating capability of a system (especially an aircraft)
    “test pilots try to push the envelope”
  5. a natural covering made out of liquid or gas
    “The spacecraft detected an envelope of gas around the comet.”
  6. a curve that is tangent to each of a family of curves