jabber vs speak

jabber is a noun but speak is not a noun.

Word	Noun	Adjective	Verb	Adverb
jabber	Yes	No	Yes	No
speak	No	No	Yes	No

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

Other hypernyms of jabber include mouth, talk, utter, verbalise, verbalize.

jabber (noun)	speak (noun)
rapid and indistinct speech

jabber (verb)	speak (verb)
talk in a noisy, excited, or declamatory manner	express in speech
	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound