thyrotoxin

1. A hypothetical substance formerly believed to be an abnormal product of diffusely hyperplastic thyroid glands in persons with Graves disease, and presumed to be the cause of the distinctive signs and symptoms of that condition (in contrast to simple hyperthyroidism). 2. A complement-fixing antigenic factor associated with certain diseases of the thyroid gland. 3. Rarely used term referring to any material toxic to thyroidal tissue.