Æsir

The Æsir are the gods of the principal pantheon in Old Norse religion and Norse mythology. The second Norse pantheon is the Vanir, these two pantheons waged war against each other, resulting in a unified pantheon.
Etymology.
"Æsir" is the plural of "áss", "ǫ́ss" "god". In genitival compounds, it takes the form ', e.g. in ' ("Thor of the Æsir"), besides ' found in "ás-brú" "gods' bridge" (the rainbow), ', ' "gods' kin", ' "gods' leader", ' "gods' might" (especially of Thor), ' "divine wrath" etc. ' "national god" (') is a title of Thor, as is ' "almighty god", while it is Odin who is "the" '. There is also Old East Norse dialectal *"ās-ækia" (OWN: *"áss-ekja"), i.e. "god ride" (Thor riding in his wagon), resulting in the modern Swedish word for atmospheric thunder – "åska" (the form "åsekia" attested as late as the 17th c.).
The feminine form is ' (plural '). The feminine suffix ' (Proto-Norse: -"unjō") is known from a few other nouns denoting female animals, such as ' "female monkey", "" "she-wolf". A cognate word for "goddess" is not attested outside Old Norse, and a corresponding West Germanic word would have been separately derived with the feminine suffixes -"inī" or -"injō".
"Áss" is attested in other Germanic languages, such as Old English (plural '), denoting a deity in Anglo-Saxon paganism, preserved only as a prefix ' in personal names (e.g. Osborne, Oswald) and some place-names, and as the genitive plural ' (' and "," "the shots of anses and of elves", i.e. "elfshot", "").
In Old High German, Old Dutch and Old Saxon, the word is only attested in personal and place names, e.g. Ansebert, Anselm, Ansfrid, Vihans. The Old High German is reconstructed as *', plural *'.
Gothic has ' as reported by Jordanes, who wrote in the 6th century CE, presumably a Latinized form of actual plural '), as a name for euhemerized semi-divine early Gothic rulers.
The reconstructed Proto-Germanic form is ' (plural '). The ansuz rune, , was named after the Æsir. *"ansuz", itself comes from Proto-Indo-European *"h₂énsus" (gen. ') "life force" (cf. Avestan "aŋhū" "lord; lifetime", "ahura" "godhood", Sanskrit "ásu" "life force", "ásura" "demons" ( *'). It is widely accepted that this word is further related to *""- "to engender" (cf. Hittite "hass-" "to procreate, give birth", Tocharian B "ās-" "to produce").
Norse mythology.
The interaction between the Æsir and the Vanir has provoked an amount of scholarly theory and speculation. While other cultures have had "elder" and "younger" families of gods, as with the Titans versus the Olympians of ancient Greece, the Æsir and Vanir were portrayed as contemporaries. The two clans of gods fought battles, concluded treaties, and exchanged hostages (Freyr and Freyja are mentioned as hostages).
An áss like Ullr is almost unknown in the myths, but his name is seen in a lot of geographical names, especially in Sweden, and may also appear on the 3rd century Thorsberg chape, suggesting that his cult was widespread in prehistoric times.
The names of the first three Æsir in Norse mythology, Vili, Vé and Odin all refer to spiritual or mental state, "vili" to conscious will or desire, "vé" to the sacred or numinous and "óðr" to the manic or ecstatic.
Æsir and Vanir.
A second clan of gods, the "Vanir", is also mentioned in Norse mythology: the god Njörðr and his children, Freyr and Freyja, are the most prominent Vanir gods who join the Æsir as hostages after a war between Æsir and Vanir. The Vanir appear to have mainly been connected with cultivation and fertility and the Æsir were connected with power and war.
In the "Eddas", however, the word "Æsir" is used for gods in general, while "Asynjur" is used for the goddesses in general. For example, in the poem Skírnismál, Freyr was called "Prince of the Æsir". In the Prose Edda, Njörðr was introduced as "the third among the Æsir", and among the Asynjur, Freya is always listed second only to Frigg.
In surviving tales, the origins of many of the Æsir are unexplained. Originally, there are just three: Odin and his brothers Vili and Vé. Odin's sons by giantesses are naturally counted as Æsir. Heimdallr and Ullr's connection with the Æsir is not clearly mentioned. Loki is a jötunn, and Njörðr is a Vanir hostage, but they are often ranked among the Æsir.
Scholarly theories and interpretations.
Given the difference between their roles and emphases, some scholars have speculated that the interactions between the Æsir and the Vanir reflect the types of interaction that were occurring between social classes (or clans) within Norse society at the time. According to another theory, the Vanir (and the fertility cult associated with them) may be more archaic than that of the more warlike Æsir, such that the mythical war may mirror a half-remembered religious conflict. This argument was first suggested by Wilhelm Mannhardt in 1877 (as described in Dumézil, xxiii and Munch, 288). On a similar note, Marija Gimbutas argues that the Æsir and the Vanir represent the displacement of an indigenous Indo-European group by a tribe of warlike invaders as part of her Kurgan hypothesis. See her case in "The Living Goddess" for more details. Another historical theory is that the inter-pantheon interaction may be an apotheosisation of the conflict between the Roman Kingdom and the Sabines.
Finally, the noted comparative religion scholar Mircea Eliade speculated that this conflict is actually a later version of an Indo-European myth concerning the conflict between and eventual integration of a pantheon of sky/warrior/ruler gods and a pantheon of earth/economics/fertility gods, with no strict historical antecedents.
List of Æsir.
The Prose Edda lists both male and female gods of the Æsir, in the 34th and 35th passages of the Gylfaginning. The Gylfaginning does not include Odin in this portion, perhaps considering him outside the ranking.
Corresponding to the fourteen Æsir listed above, section 35 lists fourteen asynjur (goddesses):
"Ganglere asked: Which are the goddesses? Har answered:"
The A-rune.
The "a"-rune, ansuz, , Younger Futhark ᚬ, was probably named after the Æsir. The name in this sense survives only in the Icelandic Rune Poem as "Óss", referring to Óðinn, who is identified with Jupiter:
The name of "a" in the Gothic alphabet is "ahsa". The common Germanic name of the rune may thus have either been "ansuz" "God, one of the Æsir", or "ahsam" "ear (of corn)"
Asleikr.
The personal names Old Norse "Ásleikr" (Latinised as "Ansleicus"), Old English "Óslác" (modern "Hasluck") and Old High German "Ansleh" may continue the term for a sacrificial performance for the gods in early Germanic paganism (""). Grimm's "Deutsches Wörterbuch" (s.v. "Leich") compares "*laikom" to the meaning of Greek , denoting first the ceremonial procession to the sacrifice, but also ritual dance and hymns pertaining to religious ritual. Paul Herrman (1906) identified as such "*ansulaikom" the victory songs of the Batavi after defeating Quintus Petillius Cerialis in the Revolt of the Batavi in the year AD 69 according to Tacitus' account, and also the "nefarious song" accompanied by "running in a circle" around the head of a decapitated goat sacrificed to (he presumes) Wodan (Odin), sung by the Lombards at their victory celebration in 579 according to the report of Pope Gregory I ("Dialogues" ch. 28).
Ásatrú.
Ásatrú, a kind of Heathenry whose name means "faith in the Æsir", is a new religious movement of polytheistic reconstructionism based on Norse paganism. As of 2007, Ásatrú is a religion officially recognized by the governments of Denmark, Iceland, Norway, and Sweden.
Most adherents do not emphasize worship of the Æsir in particular and refer to their practice as "Forn sed/sidr/siður" meaning old customs. The Icelandic "Ásatrúarfélagið" describes "Ásatrú" as "Nordic pantheism" involving "belief in the Icelandic/Nordic folklore" including all the "spirits and entities" besides "gods and other beings" this entails.