Affinitas affinitatis

AFFINITAS AFFINITATIS. That connexion between two persons which has neither consanguinity nor affinity; as, the connexion between the husband's brother and the wife's sister. This connexion is formed not between the parties themselves, nor between one of spouses and the kinsmen of the other, but between the kinsmen of both. Ersk. Inst. B, 1, tit. 6, s. 8.