/en"veuh lohp', ahn"-/ , n.
1. a flat paper container, as for a letter or thin package, usually having a gummed flap or other means of closure.
2. something that envelops; a wrapper, integument, or surrounding cover.
3. Biol. a surrounding or enclosing structure, as a corolla or an outer membrane.
4. Geom. a curve or surface tangent to each member of a set of curves or surfaces.
5. 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.
6. the fabric structure enclosing the gasbag of an aerostat.
7. the gasbag itself.
8. Electronics. the airtight glass or metal housing of a vacuum tube.
9. the technical limits within which an aircraft or electronic system may be safely operated.
10. push the envelope , to stretch the limits, as of technological advance, social innovation, etc.
Also, envelop .
[ 1700-10; enveloppe, deriv. of envelopper to ENVELOP ]