daft

Etymology

From Middle English dafte, defte (“gentle; having good manners; humble, modest; awkward; dull; boorish”), from Old English dæfte (“accommodating; gentle, meek, mild”),, from Proto-West Germanic *daftī (“fitting, suitable”), ultimately from Proto-Indo-European *dʰh₂ebʰ- (“fitting; to fit together”). Related to Old English dafnian, dafenian (“to be fitting, appropriate, or becoming”), Russian до́брый (dóbryj, “good”). Compare silly which originally meant “blessed; good, innocent; pitiful; weak”, but now means “laughable or amusing through foolishness or a foolish appearance; mentally simple, foolish”. Unrelated to, though perhaps influenced by, daff (“fool (n.); to be foolish (v.)”) (past form daffed).

adj

1. (chiefly Britain, Ireland, Australia, New Zealand, informal) Foolish, silly, stupid.
   a daft idea
   Thou art the daftest fuill that ever I saw. / Trows thou, man, be the law to get remeid / Of men of kirk? Na, nocht till thou be deid. You are the daftest fool that ever I saw. / Trust you, man, by the law to get a remedy / From men of the church? No, not till you are dead. 1602, David Lyndesay [i.e., David Lyndsay], Ane Satyre of the Thrie Estaits, in Commendation of Vertew and Vitvperation of Vyce (in Scots), Edinburgh: Printed be Robert Charteris, →OCLC; republished as Ane Satyre of the Thrie Estaits, in Commendation of Vertew and Vitvperation of Vyce (Early English Text Society, Original Series; no. 37), [London: Published for the Early English Text Society, by N[icholas] Trübner & Co., 1869], →OCLC, lines 2008–2010, page 451
   In case you haven't heard of them [the Taipings], I must tell you that they were another of those incredible phenomena that made China the topsy-turvey mess it was, like some fantastic land from Gulliver, where everything was upside down and out of kilter. Talk about moonbeams from cucumbers; the Taipings were even dafter than that. 1985, George MacDonald Fraser, chapter 1, in Flashman and the Dragon: From the Flashman Papers, 1860, London: Collins Harvill; republished New York, N.Y.: Plume, 1987
   You haven't exactly been playing the master tactician through all this, but that seems the daftest course you could possibly have taken. 1990, Iain Pears, The Raphael Affair, London: Gollancz; republished New York, N.Y.: Harper, 2014, page 22
2. (chiefly Britain, Ireland, Australia, New Zealand, informal) Crazy, insane, mad.
   The boy gathered himself up, shook his shaggy head, and, said, in a piteous tone: 'Davie's daft!' 'Davie's daft!' He then kicked the poor idiot till his cries attracted the attention of the guests, some of whom immediately came to the spot: […] 1843 April, “The Vale of Glencoe: A Tale of Scotland”, in The Knickerbocker, or New-York Monthly Magazine, volume XXI, number 4, New York, N.Y.: Published by John Allen,[…], →OCLC, page 339
   ‘It’s a lee [lie],’ says the man; ‘she’s either drunk or daft.’ / ‘Me drunk, you ill-tongued vagabond!’ says my Auntie Kirsty, who couldna bear such a reproach on her good name, ‘I’m a’ but blackfasting this day from either meat or drink; you had better no meddle wi’ my character.’ 1876, S[arah] R. Whitehead, “On the Wrong Coach”, in Daft Davie and Other Sketches of Scottish Life and Character, London: Hodder and Stoughton,[…], →OCLC, page 220
3. (obsolete) Gentle, meek, mild.
   There's mirth in the barn and the ha', the ha', / There's mirth in the barn and the ha': / There's quaffing and laughing, / And dancing and daffing; / And our young bride's daftest of a', of a', / And our young bride's daftest of a'. 1825, “Who’s at My Window”, in Allan Cunningham, compiler, The Songs of Scotland, Ancient and Modern; […] In Four Volumes, volume III, London: Printed for John Taylor,[…], →OCLC, page 334