discourse vs talk shop

discourse is a noun but talk shop is not a noun.

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

As verbs, talk shop is a hyponym of discourse; that is, talk shop is a word with a more specific, narrower meaning than discourse:

Other hyponyms of discourse include descant.

discourse (noun)	talk shop (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)

discourse (verb)	talk shop (verb)
talk at length and formally about a topic	discuss matters that are related to work
carry on a conversation
to consider or examine in speech or writing