The Collaborative International Dictionary of English v.0.48:

Yama \Ya"ma\, n. [Skr. yama a twin.] (Hindoo Myth.)
   The king of the infernal regions, corresponding to the Greek
   Pluto, and also the judge of departed souls. In later times
   he is more exclusively considered the dire judge of all, and
   the tormentor of the wicked. He is represented as of a green
   color, with red garments, having a crown on his head, his
   eyes inflamed, and sitting on a buffalo, with a club and
   noose in his hands.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Yama
    n 1: Hindu god of death and lord of the underworld