*mitra (Proto-Indo-Iranian, nominative *mitras) was an important Indo-Iranian divinity. Following the prehistoric cultural split of Indian and Iranian cultures, names descended from *mitra were used for the following religious entities:
Mitra (Sanskrit ), a deity (asura) who appears frequently in the ancient Indian text of the Rigveda.
Mithra (Avestan Mi?ra-, Mi?r?), a yazata mentioned in the Zoroastrian sacred scripture of the Avesta, whose modern Persian equivalent is Mehr.
Mithras, the principal figure of the Greco-Roman religion of Mithraism.
Both Vedic Mitra and Avestan Mithra derive from an Indo-Iranian common noun *mitra-, generally reconstructed to have meant "covenant, treaty, agreement, promise." This meaning is preserved in Avestan mi?ra "covenant." In Sanskrit and modern Indo-Aryan languages, means "friend," one of the aspects of binding and alliance.The Indo-Iranian reconstruction is attributed to Christian Bartholomae (fasc., 1979, Berlin: de Gruyter)