gibber vs speak

gibber is a noun but speak is not a noun.

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

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

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

gibber (noun)	speak (noun)
unintelligible talking

gibber (verb)	speak (verb)
speak (about unimportant matters) rapidly and incessantly	express in speech
chatter inarticulately; of monkeys	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound