The Collaborative International Dictionary of English v.0.48:

Itch \Itch\ ([i^]ch), v. i. [imp. & p. p. Itched ([i^]cht); p.
   pr. & vb. n. Itching.] [OE. icchen, [yogh]icchen, AS.
   giccan; akin to D. jeuken, joken, G. jucken, OHG. jucchen.]
   [1913 Webster]
   1. To have an uneasy sensation in the skin, which inclines
      the person to scratch the part affected.
      [1913 Webster]

            My mouth hath itched all this long day. --Chaucer.
      [1913 Webster]

   2. To have a constant desire or teasing uneasiness; to long
      for; as, itching ears. "An itching palm." --Shak.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. Any itching eruption.
      [1913 Webster]

   3. A sensation in the skin occasioned (or resembling that
      occasioned) by the itch eruption; -- called also
      scabies, psora, etc.
      [1913 Webster]

   4. A constant irritating desire.
      [1913 Webster]

            An itch of being thought a divine king. --Dryden.
      [1913 Webster]

   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 (Zool.), 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. (Zool.) 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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

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, itch]
    2: a strong restless desire; "why this urge to travel?" [syn:
       urge, itch]
    3: an irritating cutaneous sensation that produces a desire to
       scratch [syn: itch, itchiness, itching]
    v 1: scrape or rub as if to relieve itching; "Don't scratch your
         insect bites!" [syn: rub, scratch, itch]
    2: have or perceive an itch; "I'm itching--the air is so dry!"
    3: cause to perceive an itch; "his skin itched"
    4: have a strong desire or urge to do something; "She is itching
       to start the project"; "He is spoiling for a fight" [syn:
       itch, spoil]

Moby Thesaurus II by Grady Ward, 1.0:

118 Moby Thesaurus words for "itch":
   ache, acne, acne vulgaris, an universal wolf, andromania,
   aphrodisia, appetence, appetency, appetite, appetition,
   biological urge, bodily appetite, carnal desire, concupiscence,
   coveting, crave, craving, dermamycosis, dermatitis, dermatosis,
   desire, die, eczema, elephantiasis, epithelioma, eromania,
   eroticism, eroticomaniac, erotism, erotomania, erysipelas,
   erythema, exanthem, fidget, fleshly lust, furor uterinus,
   goatishness, gynecomania, hanker, hankering, have the fidgets,
   heat rash, herpes, herpes simplex, herpes zoster, hives, horniness,
   hot blood, hot pants, hunger, impetigo, indecency,
   infantile sexuality, irritation, itchiness, itching, jerk, jig,
   jigger, jigget, jiggle, jungle rot, lasciviousness, leprosy,
   libidinousness, lichen, lichen primus, lickerishness, longing,
   lupus, lupus vulgaris, lust, lustfulness, mania, miliaria,
   nymphomania, passion, pemphigus, pine, polymorphous perversity,
   prick, prickle, prickling, prickly heat, pruigo, prurience,
   pruriency, pruritus, psora, ringworm, satyriasis, satyrism,
   scabies, scratch, sexual desire, sexual longing, sexual passion,
   shingles, sigh, skin cancer, sting, tetter, thirst, thrill, tickle,
   tickling, tingle, tingling, twitch, urge, vellicate,
   venereal appetite, want, wish, yearn, yearning, yen, yeuk



The Devil's Dictionary (1881-1906):

ITCH, n.  The patriotism of a Scotchman.