discourse (up)on (something)
To talk about something at length. If he discourses about this abstract theory any longer, I'm going to fall asleep.
See also: discourse
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
someone or something to lecture about someone or something. (Upon is formal and less commonly used than on.) I would like to discourse upon this matter awhile. The committee chose to discourse on Tom and his latest fiasco rather than deal with the budgetary problems it faces.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.