in Law, as distinguished from consanguinity, is applied to the relation which each party to a marriage, the husband and the wife, bears to the kindred of the other. The marriage by making them one person is presumed to have given them the same kindred. Thus the wife's sister is the husband's sister, and the husband's brother is the wife's brother in affinity. But the relation is only with the married parties themselves, and does not bring those in affinity with them in affinity with each other: so a wife's sister has no affinity to her husband's brother. The subject is chiefly important from the matrimonial prohibitions which the canon law has applied to relations by affinity. Taking the table of degrees within which marriage is prohibited on account of consanguinity, the rule has been thus extended to affinity, and it has been maintained that wherever relationship to a man himself would be a bar to marriage, relationship to his deceased wife will be the same bar, and vice versa on the husband's decease. This rule has been founded on scriptural interpretations, chiefly of the eighteenth chapter of Leviticus, which have been subject to much discussion. Formerly by law in England, marriages within the degrees of affinity were not absolutely null, but they were liable to be annulled by ecclesiastical process during the lives of both parties. By an act passed in 1835 (5th and 6th Will. IV., c. 54), all marriages of this kind not disputed before the passing of the Act are declared absolutely valid, while all subsequent to it are declared null. This renders null in England a marriage with a deceased wife's sister or niece. The Act does not extend to Scotland, and it is a matter of doubt whether marriages within the degrees of affinity corresponding to the prohibited degrees of consanguinity are there null.

Affinity is also used to denote conformity or agreement. Thus we say, the affinity of languages, the affinity of words, the affinity of sounds, &c.

Chemistry, a term employed to express that peculiar propensity which the particles of matter have to unite and combine with each other exclusively, or in preference to any other connection.—The attractions between bodies at insensible distances, and which of course are confined to the particles of matter, have been distinguished by the name of affinity; while the term attraction has been more commonly confined to cases of sensible distance.