wed-
“to wet, to be moist”wet, moist
PIE root meaning to wet or be moist. Source of English "water," "wet," Latin unda, and Greek hýdōr.
Discussion
The root *wed- ("to wet, to be moist") is treated in Pokorny (IEW 78–81) and LIV². The simple CeC- structure lacks a laryngeal, as confirmed by the short-vowel reflexes across branches. The root underlies one of the most fundamental semantic fields: water and wetness.
The most productive descendant is the noun *wódr̥ (genitive *udéns), "water," which gives an extraordinary cognate set: English water (from Old English wæter, from Proto-Germanic *watōr), Greek húdōr (ὕδωρ, "water"), Sanskrit udán- ("water, wave"), Latin unda ("wave"), Old Church Slavonic voda ("water"), Hittite wātar, and Lithuanian vanduõ. The English-Greek pair water/hydro is a classic demonstration of Grimm's Law (*w preserved, *d > *t in Germanic).
Greek húdōr generated the productive combining form hydro-, giving English hydrate, hydraulic, hydrogen, hydrophobia, dehydrate, and hundreds of scientific terms. Latin unda ("wave") yields English undulate, inundate, abundant ("overflowing"), and redundant.
In Germanic, beyond water itself, Old English wǣt ("wet") and the verb wǣtan continue the adjectival derivative. Winter may ultimately derive from a form meaning "wet season" (*wed-en-, "watery time"), though alternative etymologies from *weyd- ("white") exist.
The Russian vodá (вода, "water") and its diminutive vodka ("little water") are among the most recognizable Slavic descendants. Old Irish uisce ("water"), giving whiskey via uisce beatha ("water of life"), is the Celtic reflex.
The root's ablaut pattern (*wed-/*wod-/*ud-) is fully regular, and its preservation across every major branch confirms that this is core PIE vocabulary of the highest antiquity.
Notes
Source of English "wet", "water" (*wódr̥). Fundamental PIE water root.