The Collaborative International Dictionary of English v.0.48:

Excellency \Ex"cel*len*cy\, n.; pl. Excellencies.
   1. Excellence; virtue; dignity; worth; superiority.
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            His excellency is over Israel.        --Ps. lxviii.
                                                  34.
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            Extinguish in men the sense of their own excellency.
                                                  --Hooker.
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   2. A title of honor given to certain high dignitaries, esp.
      to viceroys, ministers, and ambassadors, to English
      colonial governors, etc. It was formerly sometimes given
      to kings and princes.
      [1913 Webster]