The silent b in debt was added by scholars who wanted the word to look more Latin.
The English word debt comes from the Old French dette, which derived from the Latin debitum, meaning that which is owed, from the past participle of debere, to owe.1 When the word entered English in the thirteenth century, it was spelled dette, without a silent b.
Renaissance scholars, eager to align English words with their Latin origins, reinserted the b to make the word resemble debitum more closely. The spelling changed. The pronunciation did not. The b in debt has been silent for its entire life in the language.2
The anthropologist David Graeber argued in Debt: The First 5,000 Years that debt preceded money by thousands of years. Sumerian temple records from 3500 BCE document elaborate credit systems. Mesopotamian societies tracked obligations on clay tablets long before anyone minted a coin.3
Graeber observed that the moral language surrounding debt, the insistence that debts must always be repaid, obscured the historical reality that large-scale debt cancellations had been a regular feature of ancient economies. Sumerian and Babylonian rulers periodically declared clean slates, wiping out debts to prevent social collapse.4
The Latin debere combined de, meaning from, with habere, meaning to have. To owe was literally to have something from someone, a phrasing that encoded the relationship between debtor and creditor into the structure of the word itself.5
The same Latin root produced debit, the accounting term for money owed, and due, the word for an obligation or payment expected. English also borrowed the doublet duty from the same family, through Anglo-French dueté. What a person owes, what a person must pay, and what a person is obligated to do all trace back to the same Latin verb.6