Definition of envelope
1
: a flat usually paper container (as for a letter)
3a
: the outer covering of an aerostat
b
: the bag containing the gas in a balloon or airship
4a
: a natural enclosing covering (such as a membrane, shell, or integument)
b
: a lipoprotein unit membrane that forms the outer layer of some virions
5a
: a curve tangent to each of a family of curves
b
: a surface tangent to each of a family of surfaces
6
: a set of performance limits (as of an aircraft) that may not be safely exceeded
also
: the set of operating parameters that exists within these limits
7
: a conventionally accepted limit
new computers that push the envelope
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Merriam-Webster unabridged
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Time Traveler for envelope
The first known use of envelope was circa 1714
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