- affinity
- c.1300, "relation by mariage" (as opposed to consanguinity), from O.Fr. afinité, from L. affinitatem (nom. affinitas) "neighborhood, relationship by marriage," from affinis "adjacent," also "kin by marriage," lit. "bordering on," from ad- "to" + finis "a border, an end." Used figuratively since c.1600 of structural relationships in chemistry, philology, etc. Meaning "natural attraction" (as though by family) is from 1616.