Kira can be used as a Japanese name, but it isn't actually a Japanese word. The closest is "kirakira", which means "shining" or "glittering".
"Kira" is just the transliteration of the English word "killer", not a direct translation (and technically it should end in a double A). The word for killer/murderer is "hitogoroshi". I assume the confusion is because of its usage in Death Note.