1
general::
Phrase(s): one of these days
someday; in some situation like this one. • One of these days, someone is going to steal your purse if you don’t take better care of it. • You’re going to get in trouble one of these days.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.
American Heritage Idioms