foster sister
/ˈfɔstər ˌsɪstər/
noun
- A girl who is raised in the same foster family as another child, but is not biologically related to that child.
- She considers her foster-sister to be just as close as a biological sibling.
- The two girls became foster-sisters when they were placed in the same home.
- My foster-sister and I grew up together and still celebrate holidays as a family.