A Blog For Name Lovers Everywhere
And there are countless others if you are assuming it is the variant of Kai, a name that appears in a lot of places from Hawaii to Persia (Iran now).
And its a relatively uncommon name too, unlike the very similar Kai (#202 US, #56 UK, #167 The Netherlands). The only place I have been able to find Cai ranking is the UK at #349, there has been some usage in Nordic countries like Denmark and Norway but not enough for it to rank there.
Personally my favorite meaning out of these is the connection to King Arthur and his knights of the round table. What is yours?