1) The clinical syndrome that results from decreased secretion of thyroid hormone from the thyroid gland. It leads to a slowing of metabolic processes and in its most severe form to the accumulation of mucopolysaccharides in the skin, causing a nonpitting edema termed myxedema. Cretinism is the congenital form leading to abnormalities of intellectual and physical development. (Bennett, et al., Cecil Textbook of Medicine, 20th ed)

2) Too little thyroid hormone. Symptoms include weight gain, constipation, dry skin, and sensitivity to the cold. Also called underactive thyroid.