Source : Webster's Revised Unabridged Dictionary (1913)

Rash \Rash\, n. [OF. rashe an eruption, scurf, F. rache; fr.
   (assumed) LL. rasicare to scratch, fr. L. radere, rasum, to
   scrape, scratch, shave. See {Rase}, and cf. {Rascal}.] (Med.)
   A fine eruption or efflorescence on the body, with little or
   no elevation.

   {Canker rash}. See in the Vocabulary.

   {Nettle rash}. See {Urticaria}.

   {Rose rash}. See {Roseola}.

   {Tooth rash}. See {Red-gum}.

Canker rash \Can"ker rash`\ (Med.)
   A form of scarlet fever characterized by ulcerated or putrid
   sore throat.