a river bed left dry because the river has changed its course.
Words That Are Older Than You ThinkThe first citation of "OMG" in the Oxford English Dictionary appears in a 1917 letter from the British admiral John Arbuthnot Fisher to Winston Churchill.
Origin of old river
An Americanism dating back to 1685–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019