Why is the word for devil in Japanese so similar for the for bear?

悪魔 /a ku ma/ is the Word for devil and 熊 /ku ma/ is the one for bear. As you see their kanji is different, the only thing they are alike in is the pronunciation, which is no big deal since in Japanese there are numerous homonyms (Words with same pronunciation, but mostly different spellings and various meanings) and just a close pronunciation is nothing special and there is no relation between the Words.