Lewis Short
dissertātĭo (noun F) : disserto
* A spoken dissertation, discourse, disquisition (not a written treatise; cf. disputatio; late Lat.),Gell. 1, 2, 6; 10, 4, 1; 14, 3, 5 (in Plin. 10, 68, 87, § 190, the true reading is edissertatio) al.
Charlton T. Lewis, Charles Short, A Latin Dictionary