Definify.com
Webster 1913 Edition
I.O.U
I O U
,I.O.U
(ī′ ō′ ū′)
. [phonetic, from
I owe you
.] A paper having on it these letters, with a sum named, and duly signed; – in use in England as an acknowledgment of a debt, and taken as evidence thereof, but not amounting to a promissory note; a due bill.
Wharton.
Story.