Male first name (German, Low German): Kaj, Old High (Word format); origin uncertain clarified, possibly a Frisian children's linguistic shorthand of 'Gerhard', in Germany with the same variants Kai / Kaj / Kay / Cay, but from other races, even as a female Name in use Female first name (German, Scandinavian): Kaj, Old High (became independent short), origin uncertain clarified and possibly a Scandinavian countries adopted from the short form of 'Katharina', in Germany with the same variants Kai / Kaj / Kay / Cay But other sources, in use as a male name