Nusaybin (nōsĪbĭnˈ) [key] or Nisibin nēˈsĭbēn, town (1990 pop. 50,605), SE Turkey, near the Syrian border. It is a commercial and transportation center. It has ruins of the ancient Nisibis, the residence of early (2d cent. B.C.–1st cent. A.D.) Armenian kings. In early Christian times it was a center of Nestorianism. In 1839 the Egyptians defeated the Turks at Nusaybin.