noun
A formal written document in which a person swears to the truth of a statement, often used in legal or official contexts.
裁判所に宣誓書を提出した。
I submitted a written oath to the court.
この宣誓書には署名と押印が必要です。
This affidavit requires a signature and seal.
誓約書 is a written pledge or promise, often used in business or personal agreements, whereas 宣誓書 specifically involves a sworn statement of truth, typically for legal or official purposes.
Compound of 宣誓 (oath) + 書 (document). The exact historical derivation is uncertain, but the word follows a common pattern for naming official documents.