daffy (adj.)youdaoicibaDictYouDict[daffy 词源字典]
1884, perhaps from daft (adj.), or from obsolete daffe "a halfwit" (early 14c.; mid-13c. as a surname). Compare late 15c. daffish "dull-witted, spiritless." With -y (2). Related: Daffily; daffiness.[daffy etymology, daffy origin, 英语词源]
daft (adj.)youdaoicibaDictYouDict
Old English gedæfte "gentle, becoming," from Proto-Germanic *gadaftjaz (cognates: Old English daeftan "to put in order, arrange," gedafen "suitable;" Gothic gadaban "to be fit"), from PIE *dhabh- "to fit together" (see fabric). Sense of "mild, well-mannered" (c. 1200) led to that of "dull, awkward" (c. 1300). Further evolution to "foolish" (mid-15c.), "crazy" (1530s) probably was influenced by analogy with daffe "halfwit" (see daffy); the whole group probably has a common origin.