The Collaborative International Dictionary of English v.0.48:

Yenisei \Yenisei\, Yenisey \Yenisey\prop. n.
   A Russian river, flowing North into the Arctic Ocean.

   Syn: Yenisei, Yenisei River, Yenisey River.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Yenisey
    n 1: a Russian river in Siberia; rises in mountains near the
         Mongolian border and flows generally northward into the
         Kara Sea [syn: Yenisei, Yenisei River, Yenisey,
         Yenisey River]