blether vs clack

blether and clack both are nouns.

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

As verbs, clack is a hypernym of blether; that is, clack is a word with a broader meaning than blether:

blether (noun)	clack (noun)
idle or foolish and irrelevant talk	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

blether (verb)	clack (verb)
to talk foolishly	speak (about unimportant matters) rapidly and incessantly
	make a clucking sounds, characteristic of hens
	make a rattling sound