The word of 'kokumo' first appeared in an article of "Veritable Records of Three Reigns of Japan" (Nihon Sandai Jitsuroku), dated on March 25 of the third year of the Gangyo era which says 'empress to Emperor Junna demised. On that day, Kokumo made a call of condolence' when the empress to Emperor Junna, Imperial Princess Masako passed away.
『日本三代実録』の元慶3年3月25日(旧暦)（879年4月20日）条に、淳和天皇の皇后・正子内親王が崩御した時の記事として「淳和太后崩、既曰国母、可謂至尊」とあるのが初見。