c. 1300, dette, "anything owend or due from one person to another, a liability or obligation to pay or render something to another," from Old French dete, from Latin debitum "thing owed," neuter past participle of debere "to owe," originally, "keep something away from someone," from de "away" (see de-) + habere "to have" (from PIE root *ghabh- "to give or receive").
Meaning "state of being under obligation to make payment" is from mid-14c. Restored spelling after c. 1400. In Middle English, debt of the body (mid-14c.) was "that which spouses owe to each other, sexual intercourse."