Why is Jesus named the Prince of Peace instead of the King of Peace? In Isaiah 9:6, the child to be born will be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace.


  For to us a child is born, to us a son is given; and the government
  shall be upon his shoulder, and his name shall be called Wonderful
  Counselor, Mighty God, Everlasting Father, Prince of Peace.  Isaiah
  9:6 ESV


A prince is one who will one day be king, but does not currently hold that position.  Why doesn't Isaiah say that Jesus will be the King of Peace?
Before it meant the son of a king, or someone who was not yet king, the original sense of the word 'prince' was someone of the highest rank.  (It's related to the word 'principal'.) 

The Hebrew word שָׂר used in the original seems to have the same idea in it.