The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A river rising in north-central Pennsylvania and flowing about 523 km (325 mi) northwest into New York then southwest into Pennsylvania again, where it joins the Monongahela River at Pittsburgh to form the Ohio River.Word History: The Iroquois who inhabited western Pennsylvania considered the Allegheny to be the upper part of the Ohio River. Iroquois Ohio means “beautiful river” (oh-, “river”; -io, “good, fine, beautiful”). When the Delaware, an Algonquian people, moved to western Pennsylvania in the 18th century and displaced the Iroquois, they translated Iroquoian Ohio into Delaware, yielding welhik-heny, “most beautiful stream” (welhik, “most beautiful”; heny, “stream”). The name Welhik-heny was then anglicized as Allegheny.