Source : Webster's Revised Unabridged Dictionary (1913)

Nettle \Net"tle\, n. [AS. netele; akin to D. netel, G. nessel,
   OHG. nezz["i]la, nazza, Dan. nelde, n["a]lde, Sw. n["a]ssla;
   cf, Lith. notere.] (Bot.)
   A plant of the genus {Urtica}, covered with minute sharp
   hairs containing a poison that produces a stinging sensation.
   {Urtica gracitis} is common in the Northern, and {U.
   cham[ae]dryoides} in the Southern, United States. the common
   European species, {U. urens} and {U. dioica}, are also found
   in the Eastern united States. {U. pilulifera} is the Roman
   nettle of England.

   Note: The term nettle has been given to many plants related
         to, or to some way resembling, the true nettle; as:

   {Australian nettle}, a stinging tree or shrub of the genus
      {Laportea} (as {L. gigas} and {L. moroides}); -- also
      called {nettle tree}.

   {Bee nettle}, {Hemp nettle}, a species of {Galeopsis}. See
      under {Hemp}.

   {Blind nettle}, {Dead nettle}, a harmless species of
      {Lamium}.

   {False nettle} ({B[ae]hmeria cylindrica}), a plant common in
      the United States, and related to the true nettles.

   {Hedge nettle}, a species of {Stachys}. See under {Hedge}.

   {Horse nettle} ({Solanum Carolinense}). See under {Horse}.

   {nettle tree}.
   (a) Same as {Hackberry}.
   (b) See {Australian nettle} (above).

   {Spurge nettle}, a stinging American herb of the Spurge
      family ({Jatropha urens}).

   {Wood nettle}, a plant ({Laportea Canadensis}) which stings
      severely, and is related to the true nettles.

   {Nettle cloth}, a kind of thick cotton stuff, japanned, and
      used as a substitute for leather for various purposes.

   {Nettle rash} (Med.), an eruptive disease resembling the
      effects of whipping with nettles.

   {Sea nettle} (Zo["o]l.), a medusa.

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}.

Source : WordNet®

nettle rash
     n : an itchy skin eruption characterized by weals with pale
         interiors and well-defined red margins; usually the
         result of an allergic response to insect bites or food or
         drugs [syn: {urtication}, {urticaria}, {hives}]