talk about vs discourse

talk about is not a noun while discourse is a noun.

Word	Noun	Adjective	Verb	Adverb
talk about	No	No	Yes	No
discourse	Yes	No	Yes	No

As verbs, talk about and discourse are synonyms defined as:

Other synonyms of talk about include discuss.

talk about (noun)	discourse (noun)
	an extended communication (often interactive) dealing with some particular topic
	extended verbal expression in speech or writing
	an address of a religious nature (usually delivered during a church service)

talk about (verb)	discourse (verb)
to consider or examine in speech or writing	talk at length and formally about a topic
discuss or mention	carry on a conversation
	to consider or examine in speech or writing