Asura, from Sanskrit meaning a "power-seeking" and "power-hungry" being, is similar to a Titan, often, but somewhat misleading, described as a "demon"; or anaya (non-Aryan) people of ancient India. The term's derivation is uncertain. Some scholars derive it from Ashur, the Assyrian god, or from the breath (asu) of Prajapati, or from the root as (to be). According to a Hindu myth, a-sura is the negation of sura, an Indo-Aryan liquor, and refers to non-Aryan abstainers. In Hindu mythology sura came to mean a minor godin contrast to a-sura, "not-god" or "demon," but this is believed to be a false etymology.
In older part of the Rg Veda, asura refers to the supreme spirit, like the Zoroastrian Ahura Mazdah, or to Vedic deities (devas) such as Varuna, Agni, Mitra, and Indra. In younger Vedic texts and Hindu mythology asuras become demons or titans who war against the devas (gods). (cf., in the Iranian tradition ahura came to mean "god" while dacva came to mean "demon")
According to Satapathe Brahmana the devas and asuras both came from Prajapati, but the former chose true speech while the latter chose the lie. Aitarcya Brahmana relates that devas hold power by day and asuras hold equal power by night.
The non-Aryan Danavas and Laityas were called asuras. These may have been peoples who were opponents of the non-Aryans and who were mythologically equated with titans and demons.
Asuras are not necessarily evil while devas are not necessarily good. They are consubstantial, distinguished only by their mutual opposition, which is not conceived as an absolute ethical dualism. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, p. 103