The American Cyclopædia (1879)/Cognates
COGNATES, in Scotch law, collateral kindred on the mother's side, as agnates are collateral kindred on the father's side. The terms were employed in the Roman civil law somewhat differently, agnates being persons related through males only, while cognates might trace relationship through one or more female links. Thus, a brother's son was the uncle's agnate, but a sister's son was his cognate. Generally speaking, however, cognates were all who were descended from a common ancestor through a legal marriage, and the term included agnates also.