Aesir and Vanir.

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The Æsir and Vanir are the two families of Norse gods, and in the terms of Dumézil, were united after the 'war of the functions'.

I earlier posted AHD's view of the underlying IE etymology for Vanir. I repost this, along with what EIEC says about the Æsir.

EIEC u̯enh_x AHD3 *wen¹ Vanir.  This word underlies Roman 'Venus', and is represented by words for lust, copulation and procreation in many branches. The idea is pleasure, desire. It also means 'win', a prize hard-fought over, and a little oddly, 'friend', which perhaps derives from the lust-sense via the semantic concept of 'beloved', 'dear', which is also attested. AHD3 lists the English words "win, winsome, wont, wean, wish, venerate, veneral, Venus, venom, venial and venison" as reflexes. For the Vanir (Freyr, Freyja, Norðr), the association with sex and fertility completely fits the Dumézil paradigm for the war of the functions. The third function of fertility, represented by the Vanir, is united with the first two functions, that of the judicial-religious and the military. Oðinn represents the first function, while Þorr represents the second.

EIEC  h_aénsus, genitive h_ansóus AHD3 *ansu Æsir.  This is one of then Indo-European words for 'god', 'spirit', 'demon', and underlies the 'ahu-' element of Zoroastrian Ahura-Mazda. The chain in Germanic is Old Norse ōss, genitive āsir, nominative plural, æsir.

Mark.