foster son
/ˈfɔːstər sʌn/
noun
- A boy or man who is raised by a family that is not his biological or legal parents, usually for a period of time.
- They treated their foster-son as if he were their own child.
- The foster-son stayed with the family for three years before returning to his birth mother.
- She wrote a letter of thanks to the couple who had been foster-parents to her foster-son.