Definition from Wiktionary, the free dictionary
- Sense “Idle, meaningless talk” (1940), probably imitative or echoic in origin. Perhaps, but cf Greek "barbarbar” ‘unintelligible sounds’ (Grillo 1989:174).
- Adjective sense “bland, dull” (1919), perhaps influenced by French blasé (“bored, indifferent”).
- The blahs (“boredom, mild depression”) first attested 1969; extension of adjective sense and influenced by term the blues.
- Also may be connected with bleat
GRILLO, R.D. 1989. Dominant languages: Language and hierarchy in Britain and France. Cambridge: Cambridge University Press.
- (uncountable, informal) Nonsense; drivel; idle, meaningless talk.
- (informal) (in plural, the blahs) A general or ambiguous feeling of discomfort, dissatisfaction, uneasiness, boredom, mild depression, etc.
- (nonsense, drivel): bosh, bombast, bunkum, claptrap, eyewash, fustian, rant, hooey, humbug, rubbish, twaddle
- (feeling of boredom, mild depression): malaise
- (informal) Dull; uninteresting; insipid.
- Well, the new restaurant seems nice, but their menu is a little blah.
- (informal) Low in spirit or health; down.
- I decided to go exercise rather than sit around all day feeling blah.
- An expression of mild frustration.
- Blah! Why can't I get this computer to work!
- (When spoken repeatedly, often three times in succession: blah blah blah!) Imitative of idle, meaningless talk; used sometimes in a slightly derogatory manner to mock or downplay another's words, or to show disinterest in a diatribe, rant, instructions, unsolicited advice, parenting, etc. Also used when recalling and retelling another's words, as a substitute for the portions of the speech deemed irrelevant.
- Yeah, yeah, blah blah blah, Mom, you said this all yesterday.
- And then he was like, "Oh, my brother's an Internet millionaire, blah blah blah." Like I care!
- Representing the sound of vomiting. See bleah, bleh.
- (boring content): yada yada yada
expression of mild frustration
imitative of meaningless talk
- The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Wiktionary:Entry layout#Translations.
- (intransitive) To utter idle, meaningless talk.
2014, Shelagh Stephenson, Ancient Lights, page 28:
- Ooh, I feel so guilty, I've got far too much money — […] So give it away, endow a charitable foundation, burn it, but stop blahing on about it […]
- 2015, Tony Blair, Jeremy Corbyn’s politics are fantasy – just like Alice in Wonderland (in The Guardian, 29 August 2015) 
- Someone else said to me: “If you’re writing something again, don’t blah on about winning elections; it really offends them.”