blah (n.)youdaoicibaDictYouDict[blah 词源字典]
"idle, meaningless talk," 1918, probably echoic; the adjective meaning "bland, dull" is from 1919, perhaps influenced by French blasé "bored, indifferent." The blahs "depression" is attested by 1966.[blah etymology, blah origin, 英语词源]