Cognately is a rare word which means that two or more things are related by blood or marriage. Therefore, there are only a few synonyms for this word. One of them is "consanguineous," which refers to individuals who are related by blood or descended from the same ancestor. Another synonym is "affinal," which means people who are related by marriage. Conversely, "agnate" refers to male relatives who are descended from a common ancestor, while "enate" is used to describe female relatives. In summary, while cognately may not have many synonyms, these few alternatives can help you to more clearly express familial relationships in your writing.