The Collaborative International Dictionary of English v.0.48:

Machinator \Mach"i*na`tor\, n. [L.]
   One who machinates, or forms a scheme with evil designs; a
   plotter or artful schemer. --Glanvill. Sir W. Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

machinator
    n 1: a member of a conspiracy [syn: conspirator,
         coconspirator, plotter, machinator]