blether vs blabber

blether and blabber both are nouns.

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

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

Other hypernyms of blether include blab, chatter, clack, gabble, gibber, maunder, palaver, piffle, prate, prattle, tattle, tittle-tattle, twaddle.

blether (noun)	blabber (noun)
idle or foolish and irrelevant talk	one who reveals confidential information to the police or other authority

blether (verb)	blabber (verb)
to talk foolishly	speak (about unimportant matters) rapidly and incessantly