O.Ni.
Defined in 1 dictionary — Black's (1910)
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
It was the course of the English exchequer, as soon as the sheriff entered into and made up his account for issues, amerciaments, etc., to mark upon each head "O. NL," which denoted oneratur, nisi habeat sufficientem exonerationem, and presently he became the king's debtor, and a debet was set upon his head; whereupon the parties paravaile became debtors to the sheriff, and were discharged against the king, etc. 4 Inst. 116; Wharton.