WordNet sense 1 (an address of a religious nature (usually delivered during a church service)):

sermon, preaching

WordNet sense 2 (an extended communication (often interactive) dealing with some particular topic):

discussion, treatment

WordNet sense 3 (to consider or examine in speech or writing):

discuss, talk about

WordNet sense 4 (carry on a conversation):

converse, converse

WordNet sense 5 (talk at length and formally about a topic):

dissertate, hold forth