afinitas

Afinitas is a Latin noun meaning affinity, kinship, or a close relationship, often extending to notions of similarity or natural attraction. The term derives from the Latin adjective affinis, meaning near or related, with the abstract noun formed by the suffix -itas. In classical and medieval Latin, afinitas was used to denote familial or social connections and, in legal contexts, bonds established by blood or marriage.

Historically, afinitas appeared in Roman law and scholarly Latin to describe kinship by blood (consanguinity) or by marriage (affinity), as well as closer ties by similarity of character or function. The concept carried both social and legal weight, shaping permissions and prohibitions around unions and duties within communities.

In modern English, the standard term is affinity, and afinitas is most often encountered in translations of Latin sources or in discussions of historical legal concepts. The core senses—attraction or closeness between entities, whether people, substances, or ideas—are retained across languages. In science, related ideas are expressed as affinity: chemical affinity (tendency of substances to react), biological binding affinity (strength of interactions such as antigen–antibody), and metaphoric uses describing compatibility between individuals or groups.

In canon law and related religious contexts, affinity denotes the relationships created by marriage that restrict certain marriages, distinct from blood kinship. In mathematics and geometry, the related term affine describes transformations preserving parallelism, a linguistic descendant of the same root, though the Latin form afinitas is rarely used in that setting today.

See also: affinity, kinship, bonding, similarity, affine transformation.