What is Affiance?

Legal Definition
Contracts. From affidare or dare fidem, to give a pledge. A plighting of troth between a man and woman. Litt. s. 39. Pothier, Traite du Mariage, n. 24, defines it to be a an agreement by which a man and a woman promise each other that they will marry together. This word is used by some authors as synonymous with marriage. Co. Litt. 34, a, note 2. See Dig. 23, 1 Code 5, 1, 4; Extrav. 4, 1.
-- Bouviers Law Dictionary
Legal Definition
A plighting of troth between man and .woman. Litt. ยง 39. An agreement by which a man or woman promise each other that they will marry together. Poth. Trait6 du Mar. n. 24.
-- Black's Law Dictionary