Also, one day; some day. On some day in the future, as in One of these days I'm going to clean out my desk, or One day you'll see what it's like to have your child insult you, or They hoped to buy a brand-new car some day. [Mid-1500s] Also see one of those days.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.