Actually, "chaos" can be used to denote more than one shade of meaning. There's scientific chaos, in the sense of "chaos theory" which is more about unpredictability of systems, etc., and there's also the sense of chaos as in chaotic mess, which is in fact more of the sense of "disorderly". So depending on the sense you intend, chaos CAN mean disorder.
That's the problem with English; words can mean more than one thing, depending on context and intent. Go figure!