Source : Webster's Revised Unabridged Dictionary (1913)

Suzerainty \Su"ze*rain*ty\, n. [F. suzerainet['e].]
   The dominion or authority of a suzerain; paramount authority.

Source : WordNet®

suzerainty
     n 1: the position or authority of a suzerain; "under the
          suzerainty of..."
     2: the domain of a suzerain