From 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]
From 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]