envelope

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A flat paper container, especially for a letter, usually having a gummed flap.
• noun Something that envelops; a wrapping.
• noun Biology An enclosing structure or cover, such as a membrane or the outer coat of a virus.
• noun The bag containing the gas in a balloon or airship.
• noun The set of limitations within which a technological system, especially an aircraft, can perform safely and effectively.
• noun A usually spherical region of interstellar matter surrounding a forming star and interacting with the star's gravitational and radiation fields.
• noun The coma of a comet.
• noun Mathematics A curve or surface that is tangent to every one of a family of curves or surfaces.
• idiom (push the envelope) To exceed or try to exceed the existing limits of a discipline or activity.

from the GNU version of the Collaborative International Dictionary of English.

• noun That which envelops, wraps up, encases, or surrounds; a wrapper; an inclosing cover; esp., the cover or wrapper of a document, as of a letter.
• noun (Astron.) The nebulous covering of the head or nucleus of a comet; -- called also coma.
• noun (Fort.) A work of earth, in the form of a single parapet or of a small rampart. It is sometimes raised in the ditch and sometimes beyond it.
• noun (Geom.) A curve or surface which is tangent to each member of a system of curves or surfaces, the form and position of the members of the system being allowed to vary according to some continuous law. Thus, any curve is the envelope of its tangents.
• noun A set of limits for the performance capabilities of some type of machine, originally used to refer to aircraft; -- it is often described graphically as a two-dimensional graph of a function showing the maximum of one performance variable as a function of another. Now it is also used metaphorically to refer to capabilities of any system in general, including human organizations, esp. in the phrase push the envelope. It is used to refer to the maximum performance available at the current state of the technology, and therefore refers to a class of machines in general, not a specific machine.
• noun to increase the capability of some type of machine or system; -- usually by technological development.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb nonstandard Alternative spelling of envelop.
• noun A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing.
• noun Something that envelops; a wrapping
• noun A bag containing the lifting gas of a balloon or airship; fabric that encloses the gas-bags of an airship.
• noun geometry A mathematical curve, surface, or higher-dimensional object that is the tangent to a given family of lines, curves, surfaces, or higher-dimensional objects.
• noun electronics A curve that bounds another curve or set of curves, as the modulation envelope of an amplitude-modulated carrier wave in electronics.
• noun music The shape of a sound, which may be controlled by a synthesizer or sampler.
• noun computing The information used for routing an email that is transmitted with the email but not part of its contents.
• noun biology An enclosing structure or cover, such as a membrane.
• noun engineering The set of limitations within which a technological system can perform safely and effectively.
• noun The nebulous covering of the head or nucleus of a comet; a coma.
• noun An earthwork in the form of a single parapet or a small rampart, sometimes raised in the ditch and sometimes beyond it.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a flat (usually rectangular) container for a letter, thin package, etc.
• noun any wrapper or covering
• noun a natural covering (as by a fluid)
• noun the bag containing the gas in a balloon
• noun the maximum operating capability of a system (especially an aircraft)
• noun a curve that is tangent to each of a family of curves