The Aesir (pronounced “ICE-ear”; Old Norse Æsir for multiple gods, Ásynjur for multiple goddesses, Áss for one god, and Ásynja for one goddess) were one of the two main tribes of deities venerated by the pre-Christian Norse and other Germanic peoples. (The second tribe was the Vanir.) Most of the best-known Norse gods and goddesses belong to the Aesir, including Odin, Thor, Frigg, Tyr, Loki, Baldur, Heimdall, Idun, and Bragi. Their home is Asgard, one of the Nine Worlds, which is located in the highest, sunniest branches of the world-tree Yggdrasil. In the Norse sources, Odin, the “Allfather,” is their chief. However, this is likely a relatively late development, and several convergent lines of evidence suggest that this role was originally occupied by Tyr.
The word “Aesir” is almost certainly derived from one of two Proto-Germanic words: *ansaz, “pole, beam, rafter,” or *ansuz, “life, vitality.” In either case, we see that the Aesir were thought of as being the powers that hold the cosmos together, the animating personalities of the “forces of nature.” (See Pantheism and Animism.)
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 Orel, Vladimir. 2003. A Handbook of Germanic Etymology. p. 20-21.