From Proto-Baltic *ūden- (or perhaps from Proto-Balto-Slavic *wandō), from the r/n-heteroclitic Proto-Indo-European noun *wódr̥, *wédōr, itself from a stem *wed- (“to moisten”). In Latvian, only the n-form of the stem survived in ūdens, but the r-form can be seen in the related term ūdrs (“otter”). The lack of initial v in Latvian also suggests that a specific dialectal term was generalized: v-initial forms can still be found in geographic names (e.g. the river Vadakste, the word vads in its dialectal senses: creek, swampy forest, etc., and place names derived from it, like Mēnešvads, Alkšņa vads, etc.). Cognates include Lithuanian vanduõ, dialectal unduõ, únduo, Old Prussian unds m, wundan n, Proto-Slavic *voda (Old Church Slavonic, Belarusian, Ukrainian, Bulgarian, Russian вода́ (vodá), Czech voda, Polish woda), Old Church Slavonic вѣдро (vědro, “small vessel”), Russian ведро́ (vedró, “bucket”), Ukrainian відро́ (vidró), Czech vědro, Polish wiadro, Proto-Germanic *watōr (Gothic 𐍅𐌰𐍄𐍉 (watō), Old High German wazzar, German Wasser, English water, wet), Hittite wātar (< *wódr̥), Sanskrit उदन् (udán), Ancient Greek ὕδωρ (húdōr), Latin unda (“wave”) (from *udn- with metathesis).