The Delawares called the site "Menachk-sink", meanining "where there is a fence or fort, or the word "Menachkhasu", meaning "a fortified place." The name "Meanock" is also given, which signified a Fortification or Fortified Town. The Seneca name, which has been variously corrupted, was Diondega, which meant "The Forks". The only Indian village at the site of Pittsburgh, at the time when the region was visited by the French and English, was Shannopin's Town. The earliest name, therefore, for the site of Pittsburgh, was probably the Seneca name Diondega.
I suggest going to read this fascinating article by George Donehoo.