Pronunciation: (en'vu-lōp", än'-),[key] —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. Also,envelop.