*Perkʷūnos

*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 connected with fructifying rains, and his name was probably invoked in times of drought. In a widespread Indo-European myth, the thunder-deity fights a multi-headed water-serpent during an epic battle in order to release torrents of water that had previously been pent up. The name of his weapon, *mel-d-(n)-, which denoted both "lightning" and "hammer", can be reconstructed from the attested traditions.

*Perkʷūnos was often associated with oaks, probably because such tall trees are frequently struck by lightning, and his realm was located in the wooded mountains, *Perkʷūnyós. A term for the sky, *h₂éḱmō, apparently denoted a "heavenly vault of stone", but also "thunderbolt" or "stone-made weapon", in which case it was sometimes also used to refer to the thunder-god's weapon.

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.