Green’s Dictionary of Slang

blither v.

to talk nonsense.

1868		F.P. Verney Stone Edge 8: ‘What did the imp come blitherin’ and botherin’ there for?’ said he .
1901		Bulletin (Sydney) 21 Dec. 22/4: Sydney D.T., after sooling-on ‘the young blood’ of N.S.W. Opposition to blither by the hour in stonewalling the tariff, now savagely turns on them thus:- [...].
1916		C.J. Dennis ‘A Gallant Gentleman’ in Moods of Ginger Mick 118: If Mick could hear me blither now, / I know jist wot ’e’d say.
1929		K.S. Prichard Coonardoo 309: You’ll have to forgive me if I blither like that occasionally.
1938		X. Herbert Capricornia (1939) 340: ‘I — I — I lost me bearin’s’, he blithers.
1942		N. Mitchison Among You Taking Notes 12–14 Dec. 221: A number of people got up and blithered, about religion, sex, the Soviet Union.
1945		J. Henderson Gunner Inglorious (1974) 36: I’ve forgotten to blither about this woman.

In derivatives

blithery (adj.)

nonsensical.

2008

R. Price Lush Life 141: Words [...] as meaningless and blithery as whatever was coming out of the television .