Words for to wash in Celtic languages.

Proto-Celtic	*nigyeti = to wash
Old Irish (Goídelc)	nigid = to wash
Irish (Gaeilge)	nigh [nʲɪɟ / n̠ʲiː] = to wash
Scottish Gaelic (Gàidhlig)	nì [ɲiː] = to wash, cleanse, purify, bathe
Manx (Gaelg)	niee = to wash, launder, bathe, pan, flush

Etymology: from the Proto-Indo-European *neygʷ- (to wash) [source].

Sources: Wiktionary, Am Faclair Beag, teanglann.ie, On-Line Manx Dictionary

Proto-Celtic	*wolk- = wet, milk
Old Irish (Goídelc)	folcaid = washes
Irish (Gaeilge)	folc(tha) = to bathe, wash, lave; pour down, shed; dip, immerse, submerge
Welsh (Cymraeg)	golchi [ˈɡɔlχɪ/ ˈɡɔlχi] = to wash, rinse; burnish; cleanse, purify; flow over or past; coat; beat, thump
Cornish (Kernewek)	golhi [‘gɔlhi] = to wash, bathe
Breton (Brezhoneg)	gwalc’hiñ = to wash

Sources: Wiktionary, teanglann.ie, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau