Amoor′ or Amur, a river of eastern Asia, 1,800 miles long. It forms a part of the boundary between Siberia and China, and flows into the Sea of Okhotsk. Length of river, including its chief tributary, the Argun, 2,800 miles, of which over 2,000 are navigable. In 1858, Russia had ceded to her the whole of the left bank of the Amur; since then, in taking possession of the Amur Valley, she has occupied much also of the right bank of the river. Amur is also a Russian province in Siberia, area 172,826 square miles; population, 119,909.