The Collaborative International Dictionary of English v.0.48:

Hives \Hives\, n. [Scot.; perh. akin to E. heave.] (Med.)
   (a) The croup.
   (b) An eruptive disease (Varicella globularis), allied to the
       chicken pox.
       [1913 Webster]

WordNet (r) 3.0 (2006):

hives
    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]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "hives":
   acne, acne vulgaris, allergen, allergic disorder, allergy, asthma,
   breaking out, conjunctivitis, cosmetic dermatitis, dermamycosis,
   dermatitis, dermatosis, diaper rash, drug rash, eczema,
   efflorescence, elephantiasis, epithelioma, eruption, erysipelas,
   erythema, exanthem, hay fever, heat rash, herpes, herpes simplex,
   herpes zoster, impetigo, itch, jungle rot, leprosy, lichen,
   lichen primus, lupus, lupus vulgaris, miliaria, nettle rash,
   papular rash, pemphigus, pollinosis, prickly heat, pruigo,
   pruritus, psora, rash, ringworm, rose cold, rupia, scabies,
   shingles, skin cancer, skin eruption, tetter, urticaria,
   vaccine rash