commercial law. The term usance comes from usage, and signifies the time which by usage or custom is allowed in certain countries, for the payment of a bill of exchange. 2. The time of one, two or three mouths after the date of the bill, according to the custom of the places between which the exchanges run. 3. Double or treble is double or treble the usual time, and half usance is half the time. Where it is necessary to divide a month upon a half usance, which is the case when the usance is for one month or three, the division, notwithstanding the difference in the length of the months, contains fifteen days.