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

Derived forms: envelopes

Type of: bag, container, cover, covering, curve, curved shape, natural covering, operating capability, performance capability, wrap, wrapper, wrapping

Part of: balloon

Encyclopedia: Envelope