The Proto-Celtic word *oino
Word *oino
Meaning one

Other words that might be of interest
*dwei ‘two’, *dwā(w) ‘two’, *swexs ‘6, six’, *nawan ‘nine, 9’, *tri ‘three, 3’, *kʷetru ‘four’, *kʷenkʷe ‘five, 5’, *sextam ‘seven’