virtual

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

• adjective Existing or resulting in essence or effect though not in actual fact, form, or name.
• adjective Existing in the mind, especially as a product of the imagination. Used in literary criticism of a text.
• adjective Computers Created, simulated, or carried on by means of a computer or computer network.

from The Century Dictionary.

• In electricity, in alternating currents, effective: said of the value which is to be used in computing energy or power relations of a current.
• In synchronous alternating-current machines, the induced electromotive force corresponding to the resultant of the magnetomotive forces of field-flux and armature-flux.
• Existing in effect, power, or virtue, but not actually: opposed to real, actual, formal, immediate, literal.
• Pertaining to a real force or virtue; potential.
• In mech., as usually understood, possible and infinitesimal: but this meaning seems to have arisen from a misunderstanding of the original phrase virtual velocity, first used by John Bernoulli, January 26th, 1717, which was not clearly defined as a volocity at all, but rather as an infinitesimal displacement of the point of application of a force resolved in the direction of that force.

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

• adjective Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing.
• adjective Being in essence or effect, not in fact.
• adjective (Mech.) the law that when several forces are in equilibrium, the algebraic sum of their virtual moments is equal to zero.
• adjective (Opt.) the point from which rays, having been rendered divergent by reflection of refraction, appear to issue; the point at which converging rays would meet if not reflected or refracted before they reach it.
• adjective (Optics) See under Image.
• adjective (Mech.) the product of the intensity of the force multiplied by the virtual velocity of its point of application; -- sometimes called virtual work.
• adjective (Mech.) a minute hypothetical displacement, assumed in analysis to facilitate the investigation of statical problems. With respect to any given force of a number of forces holding a material system in equilibrium, it is the projection, upon the direction of the force, of a line joining its point of application with a new position of that point indefinitely near to the first, to which the point is conceived to have been moved, without disturbing the equilibrium of the system, or the connections of its parts with each other. Strictly speaking, it is not a velocity but a length.
• adjective (Mech.) See Virtual moment, above.

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

• adjective In effect or essence, if not in fact or reality; imitated, simulated.
• adjective Nearly, almost. (A relatively recent corruption of meaning, attributed to misuse in advertising and media.)
• adjective Of something that is simulated in a computer or on-line.
• adjective computing, object-oriented programming In object-oriented programming, capable of being overridden with a different implementation in a subclass.
• adjective Related to technology.
• noun computing In C++, a virtual member function of a class.

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

• adjective existing in essence or effect though not in actual fact
• adjective being actually such in almost every respect