*Perkʷūnos (Proto-Indo-European: 'the Striker' or 'the Lord of Oaks') is the reconstructed name of the weather god in Proto-Indo-European mythology. The deity was 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.
*Perkʷūnos 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".
