a linguistic regionalism

I was helping a linguistics professor with his Mac the other day. Someone else came in and asked if I could look at something of hers sometime during the week. I said something like "I might can come by tomorrow."

The professor told the person, "That's an example of a linguistic regionalism."

I don't know where it's from, but I suppose Tennessee or Mississippi.

I figure that linguistic construction is my attempt to avoid making a commitment. I can come tomorrow...but maybe I can't!

(Actually, I think this contruction is called a "hedge," which makes sense)