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A tributary valley that joins a main valley where the latter has been deepened, usually by glacial erosion, resulting in a steep drop from the floor of the tributary valley to the floor of the main valley.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(Physical Geography) geography a tributary valley entering a main valley at a much higher level because of overdeepening of the main valley, esp by glacial erosion
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014