Ahura is an Avestan language designation for a particular class of Zoroastrian angelic divinities.
Avestan ahura derives from Indo-Iranian *asura, also attested in an Indian context as Rigvedic asura. As suggested by the similarity to the Old Norse æsir, Indo-Iranian *asura may have an even earlier Indo-European root.
It is commonly supposed that Indo-Iranian *Asura was the proper name of a specific divinity with whom other divinities were later identified.
For obscure reasons, the Oxford English Dictionary lists asura, rather than ahura, as a Zoroastrian term.
In the Gathas, the oldest hymns of Zoroastrianism and thought to have been composed by Zoroaster himself, the prophet exhorts his followers to pay reverence to only the ahuras and to rebuff the daevas and others who act "at Lie's command". That should not, however, be construed to reflect a view of a primordial opposition. Although the daevas would, in later Zoroastrian tradition, appear as malign creatures, in the Gathas the daevas are (collectively) gods that are to be rejected.
In the Gathas, the prophet does not specify which of the divinities other than Ahura Mazda are considered to be ahuras.
In the Fravaraneh, the Zoroastrian credo summarized in Yasna 12.1, the adherent declares: "I profess myself a Mazda worshiper, a follower of the teachings of Zoroaster, rejecting the daevas, ... " This effectively defines ahura by defining what ahura is not.
In the Younger Avesta, three divinities of the Zoroastrian pantheon are repeatedly identified as ahuric. These three are Ahura Mazda, Mithra and Apam Napat, and hence known as the "Ahuric triad". Other divinities with whom the term "Ahuric" is associated include the six Amesha Spentas and (notable among the lesser yazatas) Aredvi Sura of The Waters and Ashi of Reward and Recompense.