Named after the Monongahela River. The name Monongahela is of Native American origin; Annie Clark Miller says that it means “High banks or bluffs, falling in at many places.” A 1936 article in the Post-Gazette translates it as “high banks breaking off in some places and tumbling down.”
See also Boulevard of the Allies, which was originally to be named Monongahela Boulevard.
Miller, Annie Clark. Early Land Marks and Names of Old Pittsburgh: An address delivered before the Pittsburgh Chapter Daughters of the American Revolution at Carnegie Institute, Nov. 30, 1923. Pittsburgh Chapter Daughters of the American Revolution, 1924, p. 6. Historic Pittsburgh 00awn8211m; Internet Archive earlylandmarksna00mill.
“Street names sketch history of city: Tribute to many pioneers dimmed by time.” Pittsburgh Post-Gazette, Sept. 26, 1936, anniversary section IV, p. 16. Newspapers.com 88921069.