chat up vs talk

chat up is not a noun while talk is a noun.

Word	Noun	Adjective	Verb	Adverb
chat up	No	No	Yes	No
talk	Yes	No	Yes	No

As verbs, talk is a hypernym of chat up; that is, talk is a word with a broader meaning than chat up:

Other hypernyms of chat up include speak.

chat up (noun)	talk (noun)
	the act of giving a talk to an audience
	an exchange of ideas via conversation
	idle gossip or rumor
	a speech that is open to the public
	discussion; (`talk about' is a less formal alternative for `discussion of')

chat up (verb)	talk (verb)
talk or behave amorously, without serious intentions	express in speech
talk to someone with the aim of persuading him	exchange thoughts; talk with
	reveal information
	use language
	deliver a lecture or talk
	divulge confidential information or secrets