noun
imperial ancestors; ancestors of the Imperial Family
Formal, historical term used in contexts related to the Japanese imperial lineage. Often appears in official or ceremonial language.
皇祖皇宗の神霊に祈りを捧げる儀式が行われた。
A ceremony was held to offer prayers to the spirits of the imperial ancestors.
祖先 is a general term for ancestors, whereas 皇祖皇宗 is a specialized, formal term reserved for the imperial ancestors.
Compound of 皇祖 (こうそ, 'imperial ancestor') and 皇宗 (こうそう, 'imperial lineage/ancestors'). The exact historical derivation is uncertain; the term is conventionally associated with the founding ancestors of the Japanese imperial line.