The Collaborative International Dictionary of English v.0.48:

Tumultuate \Tu*mul"tu*ate\ (t[-u]*m[u^]l"t[-u]*[=a]t), v. i. [L.
   tumultuatus, p. p. of tumultuari to make a tumult.]
   To make a tumult. [Obs.] "He will murmur and tumultuate."
   --South.
   [1913 Webster]