1.extended verbal expression in speech or writing
2.an address of a religious nature (usually delivered during a church service)
3.an extended communication (often interactive) dealing with some particular topic;
the book contains an excellent discussion of modal logic
1.to consider or examine in speech or writing;
The article covered all the different aspects of this question
2.carry on a conversation
3.talk or hold forth formally about a topic;
The speaker dissertated about the social politics in 18th century England