"talk nonsense," 1520s, blether, Scottish, probably from a Scandinavian source such as Old Norse blaðra "mutter, wag the tongue," which is perhaps of imitative origin, or from Proto-Germanic *blodram "something inflated" (the source of bladder). Related: Blathered; blathering.
1886, "to supply with (illuminating) gas," from gas (n.1). Sense of "poison with gas" is from 1889 as an accidental thing, from 1915 as a military attack. In old slang also "talk nonsense, lie to." Related: Gassed; gassing; gasses.
1540s, "chattering gossip, flighty woman," probably a nonsense word meant to sound like fast talking; as the name of a devil or fiend it dates from c. 1600 (together with Frateretto, Hoberdidance, Tocobatto). OED lists 15 spellings and thinks flibbergib is the original.
1670s, from South African Dutch, said in old Dutch sources to be a word that means "stammerer," from hot en tot "hot and tot," nonsense words imitative of stammering. The word was applied to the people for the clicking, jerking quality of Khoisan speech. Related: Hottentotic.
"bungle, make a mess of," 1937, a respelling (perhaps euphemistic) of bollocks, from Old English beallucas "testicles," from Proto-Germanic *ball-, from PIE root *bhel- (2) "to blow, swell." The sense of it probably comes from the 20c. British use of bollocks as an interjection, "nonsense!" Related: Bollixed; bollixing.
by 1968, "buttocks, ass," U.S. slang, the kind of thing that once sounded naughty on "Laugh-In" (and briefly was popularized by that program). As it often was used with you bet your ... it may be nonsense chosen for alliteration, but there may be some whiff of biped in it.
syllables used to make nonsense refrains in songs; compare Old English la, a common exclamation; but la-la is imitative of babbling speech in many languages: Greek lalage "babble, prattle," Sanskrit lalalla as an imitation of stammering, Latin lallare "to sing to sleep, lull," German lallen "to stammer," Lithuanian laluoti "to stammer."
also applesauce, by 1739, American English, from apple + sauce (n.). The slang meaning "nonsense" is attested from 1921 and was noted as a vogue word early 1920s. Mencken credits it to cartoonist T.A. ("Tad") Dorgan. DAS suggests the word was thus used because applesauce was cheap fare served in boardinghouses.
1834, "hobby, pet project" (adjective faddy is from 1824), of uncertain origin. Perhaps shortened from fiddle-faddle. Or perhaps from French fadaise "trifle, nonsense," which is ultimately from Latin fatuus "stupid." From 1881 as "fashion, craze," or as Century Dictionary has it, "trivial fancy adopted and pursued for a time with irrational zeal."