blues (n.)youdaoicibaDictYouDict[blues 词源字典]
as a music form featuring flatted thirds and sevenths, possibly c. 1895 (though officially 1912, in W.C. Handy's "Memphis Blues"); meaning "depression, low spirits" goes back to 1741, from adjectival blue "low-spirited," late 14c.[blues etymology, blues origin, 英语词源]