Source : Webster's Revised Unabridged Dictionary (1913)

Itch \Itch\, n.
   1. (Med.) An eruption of small, isolated, acuminated
      vesicles, produced by the entrance of a parasitic mite
      (the {Sarcoptes scabei}), and attended with itching. It is
      transmissible by contact.

   2. Any itching eruption.

   3. A sensation in the skin occasioned (or resembling that
      occasioned) by the itch eruption; -- called also
      {scabies}, {psora}, etc.

   4. A constant irritating desire.

            An itch of being thought a divine king. --Dryden.

   {Baker's itch}. See under {Baker}.

   {Barber's itch}, sycosis.

   {Bricklayer's itch}, an eczema of the hands attended with
      much itching, occurring among bricklayers.

   {Grocer's itch}, an itching eruption, being a variety of
      eczema, produced by the sugar mite ({Tyrogluphus
      sacchari}).

   {Itch insect} (Zo["o]l.), a small parasitic mite ({Sarcoptes
      scabei}) which burrows and breeds beneath the human skin,
      thus causing the disease known as the itch. See Illust. in
      Append.

   {Itch mite}. (Zo["o]l.) Same as {Itch insect}, above. Also,
      other similar mites affecting the lower animals, as the
      horse and ox.

   {Sugar baker's itch}, a variety of eczema, due to the action
      of sugar upon the skin.

   {Washerwoman's itch}, eczema of the hands and arms, occurring
      among washerwomen.

Itch \Itch\, v. i. [imp. & p. p. {Itched}; p. pr. & vb. n.
   {Itching}.] [OE. icchen, ?icchen, AS. giccan; akin to D.
   jeuken, joken, G. jucken, OHG. jucchen.]
   1. To have an uneasy sensation in the skin, which inclines
      the person to scratch the part affected.

            My mouth hath itched all this long day. --Chaucer.

   2. To have a constant desire or teasing uneasiness; to long
      for; as, itching ears. ``An itching palm.'' --Shak.

Source : WordNet®

itch
     n 1: a contagious skin infection caused by the itch mite;
          characterized by persistent itching and skin irritation;
          "he has a bad case of the itch" [syn: {scabies}]
     2: a strong restless desire; "why this urge to travel?" [syn: {urge}]
     3: an irritating cutaneous sensation that produces a desire to
        scratch [syn: {itchiness}, {itching}]
     v 1: scrape or rub as if to relieve itching; "Don't scratch your
          insect bites!" [syn: {rub}, {scratch}]
     2: have or perceive an itch; "I'm itching--the air is so dry!"
     3: have a strong desire or urge to do something; "She is
        itching to start the project"; "He is spoiling for a
        fight" [syn: {spoil}]