foster brother/sistersomeone who has different parents from you, but who is being brought up in the same family 义兄[弟]/义姐[妹]foster brother/sister• The two play New York subway cops who also are foster brothers.• I shan't be able to treat you now as if you were my foster sister, Jenny.• Her foster brother's misinformation must be dispelled, but what did she say?• She knew her foster brother was unreliable.
→ foster brother/sister at foster2(3)