Perhaps the following may help: In the book entitled, "The Allegheny River-
Watershed of the Nation" by Jim Schafer and Mike Sajna, it states that, "tradition has it that there were a people here called the Allegwie for whom the Allegheny is named." In addition, James Swauger, curator emeritus of anthropology at
the Carnegie Museum of Natural History may be another resource for you to find
the exact origin of the word Allegheny.
Bonnie Bookshar, California University of PA