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1.
The act of speaking foolishly and without purpose, often annoying others in the process. Talking at length for the sake of hearing one's own voice.
The stupid twit wouldn't stop blithering about how 'deep' her favourite fad author is.
by FeO2 August 27, 2010
 
2.
often used as a prefix it "idiot", meaning incompetant
"my god, you BLITHERING IDIOT! HOW COULD YOU HAVE DONE SUCH A THING?!?!"
by all knowin' August 26, 2003
 
3.
Very Much So!
My Uncle is a blithering IDIOT! :P
by Secret Stranger(; December 26, 2009