What is the term for relatives related by marriage only?

The correct term for relatives related by marriage only is "adfines." This word specifically refers to the connection that arises through marriage, highlighting the family ties that are formed when individuals marry into each other's families. In ancient Roman society, the concept of adfines was significant, as it acknowledged the various alliances and relationships that can develop through marriage, differentiating these from blood relatives.

The other terms have different meanings. "Agnati" refers to relatives through paternal lineage, meaning blood relatives that are recognized through the male line. "Cognati" refers to those related by blood, encompassing all relatives whether they are on the maternal or paternal side. "Societas" is associated with the idea of a partnership or association, rather than family relationships. Understanding these distinctions helps clarify the specific nature of familial connections that the term "adfines" captures.