noun
Your Highness; His Highness; Her Highness
Honorific title used for imperial princes and princesses, and for certain other high-ranking royalty. Can be used as a form of address or as a reference. The reading てんが is obsolete.
皇太子殿下が式典にご出席になりました。
His Imperial Highness the Crown Prince attended the ceremony.
殿下、お言葉をいただけますか。
Your Highness, may we have a few words?
From Chinese 殿下 (diànxià), literally 'below the palace', used as a respectful indirect reference to royalty.