noncousin
Your cousins’ cousins. The nieces and nephews of your aunt/uncle that married into your family. When you uncle gets married and his wife has a sister who has kids, those aren’t your cousins. They are, however, cousins to your cousins.
My Uncle John married a woman named Jane. Jane’s sister has a son named Joe. John and Jane have a daughter named Jean. Jean is my cousin. Jean is also Joe’s cousins. Joe is not my cousin, he is my noncousin.