Words for to walk in Celtic languages.

Middle Irish (Gaoidhealg)	siblaid = to travel, traverse, proceed, move, walk; to flow; to go over, examine
Irish (Gaeilge)	siúil [ʃuːlʲ] = to walk, be able to walk; come or go on foot; move about for exercise or pleasure; step on, into; tread, travel
Scottish Gaelic (Gàidhlig)	siubhail [ʃu.al] = to travel, commute; walk, move, stroll; go, depart; die
Manx (Gaelg)	shooill = to walk, traverse, gait, pace, tread, promenade, perambulate

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

Proto-Celtic	*kerdeti = to walk
Old Irish (Gaídelc)	foceird = to put, place, set; to throw, cast
Middle Welsh (Kymraec)	kerddet [ˈkɛrðɛd] = to walk
Welsh (Cymraeg)	cerdded [ˈkɛrðɛd] = to walk, journey, travel, approach, traverse, march, go, move
Cornish (Kernewek)	kerdhes [‘kɛrðɛs / ‘kɛr(ð)ɐz] = to walk, get along
Breton (Brezhoneg)	kerzhet = to walk

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

Sources: Wiktionary, Geiriadur yr Academi, Geiriadur Prifysgol Cymru, Gerlyver Kernewek, Dictionnaire Favereau