I think it means Bounding Elk based on what I read in the Wikipedia.
Also, I doubt this to be helpful but in the medical dictionary there is Uncus a latin word. Possibly this could be a related name which derived from latin? I am unsure, however, According to the wikipedia which I see you have listed, they stated that he was known as Bounding Elk which in there language was Uncas. Hopefully I was of some help atleast!! I tried :)
Then as it was, Then again it will be and though the course will change sometimes, rivers always reach the sea !
-Zeppelin :D