Definition of Foenus unciarium
Interest of one twelfth, that is, interest amounting annually to one twelfth of the principal, hence at the rate of eight and one-third per cent, per annum. This was the highest legal rate of interest in the early times of the Roman republic. An extraordinary rate of interest agreed to be paid for the loan of money on the hazard of a voyage; sometimes called ”usura maritima.” 2 Bl.Comm. 458. The extraordinary rate of interest, proportioned to the risk, demanded by a person, lending money on a ship, or on "bottomry,” as it is termed. The agreement for such a rate of interest is also called "foenus nauticum.”
That's the definition of Foenus unciarium in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.