Lewis & Short

affīnĭtas (adf-), ātis, f. [affinis] (gen. plur. adfinitatium, Just. 17, 3), the state or condition of adfinis.

  1. I. Relationship or alliance by marriage, esp. between a father and son-in-law, Ter. And. 1, 5, 12 Ruhnk. (cf. affinis): adstringere inter aliquos, Plaut. Trin. 3, 2, 73: effugere, Ter. And. 1, 5, 12; so id. Hec. 4, 4, 101: caritas generis humani serpit sensim foras, cognationibus primum, tum adfinitatibus, deinde amicitiis, post vicinitatibus, Cic. Fin. 5, 23, 68: adfinitate se devincire cum aliquo, id. Brut. 26: cum aliquo adfinitate conjungi, Nep. Paus. 2, 3: in adfinitatem alicujus pervenire, id. Att. 19, 1: contrahere, Vell. 2, 44: facere inter aliquos, id. 2, 65: jungere cum aliquo, Liv. 1, 1: adfinitate conjunctus, allied by marriage, Suet. Ner. 35: in adfinitatis jura succedit, Just. 7, 3.
    Meton., the persons so related, like kindred in Engl.: patriam deseras, cognatos, adfinitatem, amicos, Plaut. Trin. 3, 2, 75.
  2. II. Fig., relationship, affinity, union, connection (rare), Varr. R. R. 1, 16: litterarum, Quint. 1, 6, 24: per adfinitatem litterarum, qui φώρ Graece, Latine fur est, Gell. 1, 18, 5: tanta est adfinitas corporibus hominum mentibusque, id. 4, 13, 4.