Source : Webster's Revised Unabridged Dictionary (1913)

Medium \Me"di*um\, n.; pl. L. {Media}, {E}. {Mediums}. [L.
   medium the middle, fr. medius middle. See {Mid}, and cf.
   {Medius}.]
   1. That which lies in the middle, or between other things;
      intervening body or quantity. Hence, specifically:
      (a) Middle place or degree; mean.

                The just medium . . . lies between pride and
                abjection.                        --L'Estrange.
      (b) (Math.) See {Mean}.
      (c) (Logic) The mean or middle term of a syllogism; that
          by which the extremes are brought into connection.

   2. A substance through which an effect is transmitted from
      one thing to another; as, air is the common medium of
      sound. Hence: The condition upon which any event or action
      occurs; necessary means of motion or action; that through
      or by which anything is accomplished, conveyed, or carried
      on; specifically, in animal magnetism, spiritualism, etc.,
      a person through whom the action of another being is said
      to be manifested and transmitted.

            Whether any other liquors, being made mediums, cause
            a diversity of sound from water, it may be tried.
                                                  --Bacon.

            I must bring together All these extremes; and must
            remove all mediums.                   --Denham.

   3. An average. [R.]

            A medium of six years of war, and six years of
            peace.                                --Burke.

   4. A trade name for printing and writing paper of certain
      sizes. See {Paper}.

   5. (Paint.) The liquid vehicle with which dry colors are
      ground and prepared for application.

   {Circulating medium}, a current medium of exchange, whether
      coin, bank notes, or government notes.

   {Ethereal medium} (Physics), the ether.

   {Medium of exchange}, that which is used for effecting an
      exchange of commodities -- money or current
      representatives of money.

Medium \Me"di*um\, a.
   Having a middle position or degree; mean; intermediate;
   medial; as, a horse of medium size; a decoction of medium
   strength.

Source : WordNet®

medium
     n 1: a means or instrumentality for storing or communicating
          information
     2: the surrounding environment; "fish require an aqueous
        medium"
     3: an intervening substance through which signals can travel as
        a means for communication
     4: (bacteriology) a nutrient substance (solid or liquid) that
        is used to cultivate micro-organisms [syn: {culture medium}]
     5: an intervening substance through which something is
        achieved; "the dissolving medium is called a solvent"
     6: a liquid with which pigment is mixed by a painter
     7: (biology) a substance in which specimens are preserved or
        displayed
     8: a state that is intermediate between extremes; a middle
        position; "a happy medium"
     9: someone who serves as an intermediary between the living and
        the dead; "he consulted several mediums" [syn: {spiritualist}]
     10: transmissions that are disseminated widely to the public
         [syn: {mass medium}]
     11: an occupation for which you are especially well suited; "in
         law he found his true metier" [syn: {metier}]
     [also: {media} (pl)]

medium
     adj 1: around the middle of a scale of evaluation of physical
            measures; "an orange of average size"; "intermediate
            capacity"; "a plane with intermediate range"; "medium
            bombers" [syn: {average}, {intermediate}]
     2: (of meat) cooked until there is just a little pink meat
        inside
     [also: {media} (pl)]