Your kinsman is your family member — someone who's related to you. Even if you don't know your second cousin very well, he's still your kinsman.
The noun kinsman can refer to any blood relation or ancestor, especially those who are male. You can also use kinswoman to talk about female relatives. The word is a formal one that you might come across in an anthropology textbook or a family history: "The first kinsman to leave England came on the Mayflower." Kinsman comes in part from kin, with its Old English root cynn, or "family."