blab vs clack

blab is not a noun while clack is a noun.

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

As verbs, blab and clack are synonyms defined as:

blab and clack: speak (about unimportant matters) rapidly and incessantly

blab (noun)	clack (noun)
	a simple valve with a hinge on one side; allows fluid to flow in only one direction
	a sharp abrupt noise as if two objects hit together; may be repeated

blab (verb)	clack (verb)
divulge confidential information or secrets	speak (about unimportant matters) rapidly and incessantly
speak (about unimportant matters) rapidly and incessantly	make a clucking sounds, characteristic of hens
	make a rattling sound