chat up vs speak

chat up and speak both are verbs.

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

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

Other hypernyms of chat up include talk.

chat up (verb)	speak (verb)
talk or behave amorously, without serious intentions	express in speech
talk to someone with the aim of persuading him	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound