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.
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   2. Any itching eruption.
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   3. A sensation in the skin occasioned (or resembling that
      occasioned) by the itch eruption; -- called also
      scabies, psora, etc.
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   4. A constant irritating desire.
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            An itch of being thought a divine king. --Dryden.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Psora \Pso"ra\, n. [L., fr. Gr. ?.] (Med.)
   A cutaneous disease; especially, the itch.
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