What does Kai mean?
Most commonly taken from Hawaiian 'kai', meaning 'sea' or 'ocean'. The same short sound exists independently in several languages (Japanese, Scandinavian forms of names like Kajus, and others), but its modern Western popularity leans on the Hawaiian 'sea' meaning.
What does Hoku mean?
The Hawaiian word 'hoku' (properly 'hoku') meaning 'star', recorded in the Pukui-Elbert dictionary. It appears in compounds such as Hokulani ('heavenly star') and in Polynesian star-navigation terms.