noun
official letter; personal message (from a high official)
Refers to a formal letter or message sent by a high-ranking official such as the Emperor, Prime Minister, or a head of state. Often used in diplomatic or governmental contexts.
首相は大統領に親書を送った。
The Prime Minister sent an official letter to the President.
天皇陛下の親書が大使に手渡された。
The Emperor's personal message was handed to the ambassador.
noun
handwritten letter; autograph letter
Emphasizes that the letter is written by hand, often by the sender personally. Can be used for personal correspondence, but still carries a somewhat formal tone.
彼は直筆の親書を私に送ってくれた。
He sent me a handwritten letter in his own hand.
Composed of 親 (しん, 'parent; intimate; personally') and 書 (しょ, 'writing; document'). The combination suggests a document written personally or by someone in a close, authoritative relationship.