The first element of the path of classical yoga: Restraint
Yama (restraints or attitudes): contast to niyama. Controls placed on behavior to prevent suffering. Here, as taught by a yoga teacher, so of course warped and obscured, the Yamas are the don'ts to the niyamas' dos (how does one pluralize a contraction!?)

1. Ahimsa
2. Satya
3. Asteya
4. Brahmacharya
5. Aparigraha

Yama is also supposedly Japanese for mountain. Maybe someone can verify that?

"Yama" is also the name of the hideous buffalo-headed ruler of the realm of hell ("naraka-gati") in Buddhist mythology.

Yama was a originally a king of Vaishali who, exulting in the death and suffering and destruction at the height of a bloody battle, wished that he were the king of hell so that he could always behold such sights and smell such a stench.

In accordance with this desire he was reborn as Yama. For whatever unexplained reason, his eight generals and eighty thousand of his followers appeared there as his, well, I suppose his staff.

Yama and his staff have molten copper poured down their throats three times a day. The rest of the time, they torment everyone else.

In the later Buddhist tantras, Yama is defeated and his powers subsumed and transformed by an incarnation of Manjusri, the bodhisattva of prajna, called Yamantaka.

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.

 

© Webster 1913.