I didn’t know that was a real word. But, here’s the definition from thefreedictionary.com:
intr.v. dis·ser·tat·ed also dis·sert·ed, dis·ser·tat·ing also dis·sert·ing, dis·ser·tates also dis·serts
To discourse formally.
The thesaurus entry adds:
talk at length and formally about a topic; “The speaker dissertated about the social politics in 18th century England”
This is now my new favorite word. There’s even a noun form “dissertator.”