The Collaborative International Dictionary of English v.0.48:

hyperthyroidism \hyperthyroidism\ n. (Med.)
   An abnormality of the thyroid gland characterized by the
   pathologically excessive production of thyroid hormones; --
   also, the resulting condition characterized by increased
   metabolism, weight loss, rapid heart rate, high blood
   pressure, an enlarged thyroid gland and sometimes
   exophthalmos. It leads to, and may be confirmed by, high
   plasma levels of triiodothyronine or thyroxin.

   Syn: thyrotoxicosis.
        [WordNet 1.5] Hypertrophic

WordNet (r) 3.0 (2006):

hyperthyroidism
    n 1: an overactive thyroid gland; pathologically excessive
         production of thyroid hormones or the condition resulting
         from excessive production of thyroid hormones [syn:
         hyperthyroidism, thyrotoxicosis] [ant:
         hypothyroidism]