Dr.
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
An abbreviation for "doctor;" also, in commercial usage, for "debtor," Indicating the items or particulars in a bill or In an account-book chargeable against the person to whom the bill is rendered or In whose name the account stands, as opposed to "Cr." ("credit" or "creditor"), which indicates the items for which he is given credit.
Jaqua v. Shewalter, 10 Ind. App. 234, 37 N. E. 1072.