The Collaborative International Dictionary of English v.0.48:

Urticaria \Ur`ti*ca"ri*a\, n. [NL. See Urtica.] (Med.)
   The nettle rash, a disease characterized by a transient
   eruption of red pimples and of wheals, accompanied with a
   burning or stinging sensation and with itching; uredo.
   [1913 Webster]

WordNet (r) 3.0 (2006):

urticaria
    n 1: 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, nettle rash]