IOU1

IOU1

An abbreviation of "I owe you one," with "owe," "you," and "one" represented by the O, U, and 1, respectively. Used to express gratitude and indebtedness to someone for some favor or kindness. A: "Can I borrow your car for the weekend?" B: "Sure, no problem." A: "Thanks, dude. IOU1."
Farlex Dictionary of Idioms.
See also:
  • be in (one's) debt
  • be in somebody's debt
  • debt
  • IOU
  • owe (one) a debt of gratitude
  • owe a debt of gratitude
  • owe a debt of gratitude to (someone)
  • owing
  • gratitude
  • I owe you one