step-sibling
noun [ C ] mainly UK (also mainly UK step sibling); (US usually stepsibling) uk/ˈstepˌsɪb.lɪŋ/ us/ˈstepˌsɪb.lɪŋ/
继父（或继母）的孩子，继兄弟姐妹
a child of your stepfather or stepmother with another person who is not your parent
Step-siblings have no parents in common, whereas half-siblings share one parent. 继兄弟姐妹没有共同的父母，而同父异母或同母异父的兄弟姐妹则有同一个父亲或母亲。