*ahwō

Traditionally derived from pre-Germanic *ákʷā, from Proto-Indo-European *h₂ékʷ-eh₂ (Kroonen 2013: 7; Ringe 2017: 116). Cognate with Latin aqua < Proto-Italic *akʷā; (de Vaan 2008: 48–49). The deeper status of the etymon is debated: it is a strong Germanic–Italic isogloss, but its limited distribution has led Beekes (1998: 459–61) to treat it as an Old European hydronymic substrate word rather than as an inherited Proto-Indo-European word; Kroonen (2013: 7) instead keeps the inherited analysis and connects it more broadly with the *h₂ep- river/water complex.

Prósper (2002: 396–97) provides interesting evidence for an alternative etymon in citing several deity names and epithets associated with water, attributed to Lusitanian (e.g., AGVAECO, AQVILIANICO, and AQVITIBVS). She notes that PIE *kʷ and *kw did not merge in Lusitanian: PIE *kʷ became Lusitanian *p (similar to P-Celtic and some Italic dialects) but PIE *kw remained as Lusitanian *kw (or possibly *gw) (see also (Witczak 2005: 274–76)). As a result, she posits the etymon without a labiovelar consonant, and instead with a consonant cluster, *kw, thus *h₂ék-w-eh₂. This derivation coincides with Garnier’s (2012) theory, based on *h₂éḱ-u-, comparing Latin aqua and the “swift” word-family reflected by Ancient Greek ὠκύς (ōkús), Sanskrit आशु (āśú), and Latin ōcior. This analysis is semantically attractive for Germanic, where *ahwō primarily denotes a river or stream, but the wider Indo-European connection remains uncertain, especially since the laryngeals of the “swift” adjective are disputed.