When we talk about a shirttail relation, we are referring to someone who is related to us, but only distantly or indirectly. This term is often used to describe extended family members, such as a distant cousin or an in-law that we are not particularly close to. However, there are several other synonyms that we can use to describe this type of relationship, including collateral relative, kinship by marriage, remote relation, and tangential relation. These terms all convey the idea that there is some kind of familial connection, but that it is not especially strong or meaningful. Ultimately, the term we choose to use may depend on the specific context and relationship in question.