A term, used originally in the civil law, but now generally adopted, denoting a contract in which both the contracting parties are bound to fill fill obligations reciprocally towards each other; as a contract of sale, where one becomes bound to deliver the thing sold, and the other to pay the price of it. Montpelier Seminary v. Smith, 69 Vt. 382, 38 Atl. 66. “Every convention properly so called consists of a promise or mutual promises proffered and accepted. Where one only of the agreeing parties gives a promise, the convention is said 1o be ‘unilateral.’ Wherever mutual promises are proffered and accepled. there are, in strictness, two or more conventions. But where the performance of either of the promises is made to depend on the performance of the other, the several conventions are commonly deemed one convention, and the convention is then said to be