Source : Webster's Revised Unabridged Dictionary (1913)

Supersession \Su`per*ses"sion\, n. [Cf. OF. supersession. See
   {Supersede}.]
   The act of superseding, or the state of being superseded;
   supersedure.

         The general law of diminishing return from land would
         have undergone, to that extent, a temporary
         supersession.                            --J. S. Mill.

Source : WordNet®

supersession
     n : act of replacing one person or thing by another especially
         one held to be superior [syn: {supersedure}]