The Collaborative International Dictionary of English v.0.48:

Virtual \Vir"tu*al\ (?; 135), a. [Cf. F. virtuel. See Virtue.]
   1. Having the power of acting or of invisible efficacy
      without the agency of the material or sensible part;
      potential; energizing.
      [1913 Webster]

            Heat and cold have a virtual transition, without
            communication of substance.           --Bacon.
      [1913 Webster]

            Every kind that lives,
            Fomented by his virtual power, and warmed. --Milton.
      [1913 Webster]

   2. Being in essence or effect, not in fact; as, the virtual
      presence of a man in his agent or substitute.
      [1913 Webster]

            A thing has a virtual existence when it has all the
            conditions necessary to its actual existence.
                                                  --Fleming.
      [1913 Webster]

            To mask by slight differences in the manners a
            virtual identity in the substance.    --De Quincey.
      [1913 Webster]

   Principle of virtual velocities (Mech.), the law that when
      several forces are in equilibrium, the algebraic sum of
      their virtual moments is equal to zero.

   Virtual focus (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.

   Virtual image. (Optics) See under Image.

   Virtual moment (of a force) (Mech.), the product of the
      intensity of the force multiplied by the virtual velocity
      of its point of application; -- sometimes called virtual
      work.

   Virtual velocity (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.

   Virtual work. (Mech.) See Virtual moment, above.
      [1913 Webster]

WordNet (r) 3.0 (2006):

virtual
    adj 1: being actually such in almost every respect; "a practical
           failure"; "the once elegant temple lay in virtual ruin"
           [syn: virtual(a), practical(a)]
    2: existing in essence or effect though not in actual fact; "a
       virtual dependence on charity"; "a virtual revolution";
       "virtual reality"

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "virtual":
   accepted, basic, between the lines, constructive, covert, cryptic,
   delitescent, dormant, effective, esoteric, essential, fundamental,
   hibernating, hidden, latent, lurking, muffled, mystic, obfuscated,
   obscured, occult, possible, potential, practical, sleeping,
   submerged, under the surface, underlying, understood, unmanifested,
   veiled



The Jargon File (version 4.4.7, 29 Dec 2003):

virtual
 adj.

    [via the technical term virtual memory, prob.: from the term virtual image
    in optics]

    1. Common alternative to logical; often used to refer to the artificial
    objects (like addressable virtual memory larger than physical memory)
    simulated by a computer system as a convenient way to manage access to
    shared resources.

    2. Simulated; performing the functions of something that isn't really
    there. An imaginative child's doll may be a virtual playmate. Oppose real
    .


The Free On-line Dictionary of Computing (30 December 2018):

virtual

    (Via the technical term virtual
   memory, probably from the term "virtual image" in optics)
   1. Common alternative to logical; often used to refer to the
   artificial objects (like addressable virtual memory larger
   than physical memory) created by a computer system to help the
   system control access to shared resources.

   2. Simulated; performing the functions of something that isn't
   really there.  An imaginative child's doll may be a virtual
   playmate.

   Opposite of real or physical.

   [Jargon File]

   (1994-11-30)