The Collaborative International Dictionary of English v.0.48:

Struck \Struck\,
   imp. & p. p. of Strike.
   [1913 Webster]

   Struck jury (Law), a special jury, composed of persons
      having special knowledge or qualifications, selected by
      striking from the panel of jurors a certain number for
      each party, leaving the number required by law to try the
      cause.
      [1913 Webster]