someday (adv.)

"at some indefinite future date," 1768, from some + day. As two words, in the same sense, from late 14c.

MISS SOMEDAY.

Poor Charley wooed, but wooed in vain,

From Monday until Sunday;

Still Cupid whisper'd to the swain

"You'll conquer Betsey Someday."

[The Port Folio, June 1816]