Proto-Indo-European thunder god

A Proto-Indo-European thunder god, reconstructed as *Perkʷūnos (Proto-Indo-European: 'the Striker' or 'the Lord of Oaks'), was the weather god in Proto-Indo-European mythology. The deity is thought to be associated with fructifying rains, and his name was probably invoked in times of drought. In a widely attested Indo-European mythic pattern, the thunder-deity engages in combat with a multi-headed water-serpent in order to release the life-giving waters that had been confined or obstructed.

The Proto-Indo-European thunder god was often associated with the oak tree, probably because such tall trees are frequently struck by lightning. His domain may have been conceived as the forested mountains, designated as *Perkʷūnyós. A term for the sky, *h₂éḱmō, appears to have signified a "heavenly vault of stone" (comparable to the notion of firmament), but it could also denote a "stone-made weapon" (akin to a thunderstone). In this latter sense, the word was at times employed to refer specifically to the thunder-god's weapon. Another designation for his weapon, *mel-d-(n)-, can be reconstructed from the comparative traditions. The term originally denoted the "thunder-god's hammer" and, likely by semantic extension, has come to signify "lightning".

Contrary to other deities of the Proto-Indo-European pantheon, such as *Dyēus (the sky-god), or *H₂éwsōs (the dawn-goddess), widely accepted cognates stemming from the theonym *Perkʷūnos are only attested in Western Indo-European traditions. The linguistic evidence for the worship of a thunder god under the name *Perkʷūnos as far back as Proto-Indo-European times (4500–2500 BC) is therefore less secured.