The Collaborative International Dictionary of English v.0.48:

Convocate \Con"vo*cate\, v. t. [imp. & p. p. Convocated; p.
   pr. & vb. n. Convocating.] [L. convocatus, p. p. of
   convocare to convocate; con- + vocare to call. See Vocal,
   and cf. Convoce.]
   To convoke; to call together. [Obs.] --May (Lucan).
   [1913 Webster]