n. abnormal protrusion of the eyeball, a condition commonly associated with hyperthyroidism. Exophthalmos combined with a goiter, a swelling in the neck due to an enlarged thyroid gland (exophthalmic goiter), is a prominent feature of Graves’ disease. Exophthalmos may also be the result of a tumor or infection involving the eye. It is often characterized by the appearance of a fixed stare. —exophthalmicadj.