*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, , 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, . A term for the sky, , 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 (the sky-god), or (the dawn-goddess), widely accepted cognates stemming from the theonym are only attested in Western Indo-European traditions. The linguistic evidence for the worship of a thunder god under the name as far back as Proto-Indo-European times (4500–2500 BC) is therefore less secured. The name is generally regarded as stemming from the Proto-Indo-European (PIE) verbal root ('to strike'). An alternative etymology is the PIE noun ('the oak'), attached to the divine nomenclature ('master of'). Various cognates can be found in the Latin oak-nymphs Querquetulanae (from quercus 'oak-tree'), the Germanic ferhwaz ('oak'), the Gaulish erc- ('oak') and Quaquerni (a tribal name), the Punjabi pargāi ('sacred oak'), and perhaps in the Greek spring-nymph Herkyna. The theonym thus either meant "the Striker" or "the Lord of Oaks". A theory uniting those two etymologies has been proposed in the mythological association of oaks with thunder, suggested by the frequency with which such tall trees are struck by lightning.