h₂ékʷeh₂

The reconstruction *h₂ékʷeh₂ ("water") represents a neuter collective noun, a morphological category characteristic of PIE that denotes substances or aggregates rather than individual countable entities. The double laryngeal framing of the root (*h₂...h₂) and the labialised velar *kʷ make this form phonologically distinctive. Latin aqua ("water") is the most transparent reflex, preserving the initial *h₂- as a- (the regular colouring effect of *h₂ on adjacent vowels) and the labialised velar as qu. From aqua descend aquatic, aquarium, aqueduct, aquifer, and the chemical prefix aqua-, as well as the Romance reflexes: Italian acqua, French eau (through extensive phonological reduction), Spanish agua, Portuguese água, and Romanian apă. The Germanic cognate appears not in the common noun for "water" (which derives from a different root, *wódr̥) but in the hydronymic vocabulary: Gothic aƕa ("river"), Old English ēa ("river," preserved in place names such as Eaton, "river settlement"), Old High German aha, and Old Norse á (visible in Scandinavian river names). The restriction to river names in Germanic, while the common noun derives from *wódr̥, illustrates the lexical replacement processes that complicate reconstruction. The labialised velar *kʷ undergoes different treatments in different branches: it remains as qu in Latin, becomes p in Celtic (Old Irish ech-, as in certain hydronyms), becomes k in Greek (though the direct Greek reflex of this particular root is debated), and undergoes various developments in the satem languages. The neuter collective morphology of *h₂ékʷeh₂ aligns it with other PIE substance nouns: water, like fire and certain other natural phenomena, was conceptualised in PIE grammar as an uncountable mass rather than a discrete entity. This grammatical classification has consequences for the syntactic patterns reconstructable for PIE.