The Collaborative International Dictionary of English v.0.48:

Soliloquize \So*lil"o*quize\, v. i. [imp. & p. p.
   Soliloquized; p. pr. & vb. n. Soliloquizing.]
   To utter a soliloquy; to talk to one's self.
   [1913 Webster]

WordNet (r) 3.0 (2006):

soliloquize
    v 1: talk to oneself [syn: monologuize, monologuise,
         soliloquize, soliloquise]