The Collaborative International Dictionary of English v.0.48:
Suzerainty \Su"ze*rain*ty\, n. [F. suzerainet['e].] The dominion or authority of a suzerain; paramount authority. [1913 Webster]WordNet (r) 3.0 (2006):
suzerainty n 1: the position or authority of a suzerain; "under the suzerainty of..." 2: the domain of a suzerain