adopted parents; temporary parents
Refers to parents who are not biologically related but take on a parental role, either through formal adoption or a temporary arrangement. The 'temporary' sense is less common and often context-dependent.
He was taken in by adopted parents when he was young.
In old samurai society, temporary parents sometimes became guardians of children.
Compound of 仮 (kari, 'temporary, provisional') and 親 (oya, 'parent'). The exact historical origin is uncertain, but it likely arose in contexts where a non-biological parent figure was needed temporarily or as a substitute.