blath·er / ˈbla[voicedth]ər/ (also bleth·er / ˈble[voicedth]ər/ or blith·er / ˈbli[voicedth]ər/ ) • v. [intr.] talk long-windedly without making very much sense: she began blathering on about spirituality and life after death [as n.] (blathering) now stop your blathering and get back to work. • n. long-winded talk with no real substance.

blather, blether talk nonsense. XV. orig. Sc. — ON. blaðra, f. blaðr nonsense. For the var. blether Cf. Sc. gether for gather.
Hence as sb. XVIII.