Where do you get Ou from? Last I checked it is Kaio Ken in both English and Japanese? Some new fanslation going on? I have not seen Kai-Ou-Ken anywhere on the interwebs
王 (おう) means king and is pronounce "ou" phonetically. It's a long, drawn out version of "o". In other words, "ō".
Kaioken is the English "romanji" of the Japanese 界王拳. One should refer back to native script when translating.