WordNet (r) 3.0 (2006):

giant hives
    n 1: recurrent large circumscribed areas of subcutaneous edema;
         onset is sudden and it disappears within 24 hours; seen
         mainly in young women, often as an allergic reaction to
         food or drugs [syn: angioedema, atrophedema, giant
         hives, periodic edema, Quincke's edema]