The Collaborative International Dictionary of English v.0.48:

Eczema \Ec"ze*ma\, n. [NL., fr. Gr. 'e`kzema; "ek out + zei^n to
   boil.] (Med.)
   An inflammatory disease of the skin, characterized by the
   presence of redness and itching, an eruption of small
   vesicles, and the discharge of a watery exudation, which
   often dries up, leaving the skin covered with crusts; --
   called also tetter, milk crust, and salt rheum.
   [1913 Webster]

WordNet (r) 3.0 (2006):

eczema
    n 1: generic term for inflammatory conditions of the skin;
         particularly with vesiculation in the acute stages

Moby Thesaurus II by Grady Ward, 1.0:

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