blab vs speak

blab and speak both are verbs.

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

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

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

blab (verb)	speak (verb)
divulge confidential information or secrets	express in speech
speak (about unimportant matters) rapidly and incessantly	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound