You use expressions such as Your Excellency or His Excellency when you are addressing or referring to officials of very high rank, for example ambassadors or governors.
例句
I am reluctant to trust anyone totally, Your Excellency...我不想完全相信任何人，阁下。His excellency the President will be waiting for you in the hall.总统阁下会在大厅等你。
英汉词典释义
n.
(X-)阁下(对大使、大臣、总督、主教等的尊称)
After you, your excellency.阁下，您先请。
英英词典释义
Noun
1. a title used to address dignitaries (such as ambassadors or governors); usually preceded by Your or His or Her;