a flat paper container, as for a letter or thin package, usually having a gummed flap or other means of closure.
something that envelops; a wrapper, integument, or surrounding cover.
Biology. a surrounding or enclosing structure, as a corolla or an outer membrane.
Geometry. a curve or surface tangent to each member of a set of curves or surfaces.
Radio. (of a modulated carrier wave) a curve connecting the peaks of a graph of the instantaneous value of the electric or magnetic component of the carrier wave as a function of time.
the fabric structure enclosing the gasbag of an aerostat.
the gasbag itself.
Electronics. the airtight glass or metal housing of a vacuum tube.
the technical limits within which an aircraft or electronic system may be safely operated.
Idioms for envelope
push the envelope, to stretch established limits, as in technological advance or social innovation.
Also envelop.
Origin of envelope
1700–10; <French enveloppe, derivative of envelopper to envelop
This uses a harmless virus, usually a retrovirus, that is modified to produce the same external envelope of carbohydrates and proteins as the SARS-CoV-2 virus.
Scientists to Wall Street: You don’t really understand how COVID vaccine tests work|Jeremy Kahn|August 24, 2020|Fortune
Always follow directions from official sources, like those on your absentee-ballot envelope, over ours.
Why We’re Planning For An Election Day That Could Last Months|Nathaniel Rakich (nathaniel.rakich@fivethirtyeight.com)|August 14, 2020|FiveThirtyEight
It can only look at the signatures on the envelopes and make sure they appear to be valid.
Politics Report: Down Goes One Hot-Button Ballot Measure|Andrew Keatts|July 18, 2020|Voice of San Diego
Encasing all of this plumbing and the animal cuddled against it lies the big floaty envelope of the outer house.