An adopted child (legally taken into another family); can also refer in some contexts to a son-in-law adopted into a family.
彼は大学進学を機に里親の家の養子になった。
He became an adopted child of his foster family when he went to university.
古い記録には、娘の夫を養子にした例がある。
Old records contain examples of taking a daughter's husband as an adopted son.
養子縁組の手続きを進めるには、いくつかの書類が必要だ。
Several documents are required to proceed with adoption procedures.