The Collaborative International Dictionary of English v.0.48:

Dissertate \Dis"ser*tate\, v. i. [L. dissertatus, p. p. of
   dissertare to discuss, intents, fr. disserere. See
   Dissert.]
   To deal in dissertation; to write dissertations; to
   discourse. [R.] --J. Foster.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dissertate
    v 1: talk at length and formally about a topic; "The speaker
         dissertated about the social politics in 18th century
         England" [syn: hold forth, discourse, dissertate]