I saw a BBC program about some very identifiable blades (or traditional weaponry) originating in the Pacific Rim. I remember there were bits about Samurai swords (w/ no differentiation between different types) and the keris blade.
From what I understood, the traditional method of forging a keris is to take three pieces of metal, and twist them together. From there they are beaten flat. It was the twisting of different pieces together that gave the blade the wavy profile. This was obviously a severe simplification of the process.
Also, part of the deal with a keris was that it was not merely an effective weapon and valuable heirloom, but it had great spiritual significance as well. I have also heard statements to the effect that the Filipino belief is that every blade has a demon trapped within it. Interesting similarities could be observed here between the spiritual significance of the keris & Filipino demon thingy, and the spiritual significance (and/or fear) of a witch's athame, but that would be a digression no one cares to hear.
This page sounds like it supports what I recall from that program.
Personally, I use the distinction of spelling (if not necessarily pronunciation) to determine between the difference between the traditional keris I've described above, and the moderately (or significantly, depending on your point of view, and the particular piece you're looking at) different kris that is much more common.