The mention of Daffy Duck’s debut in Dave’s 1937 words thread prompted me to check out daft in OED, where I found it was a sister-under-the-skin to deft and had a fascinating sense-development which OED compares with silly.
In early Middle English daffte , corresponding to Old English gedæfte mild, gentle, meek < Old Germanic *gadaftjo-z , < gadafti vbl. n. from stem daƀ-, in Gothic gadaban to become, be fit, Old English past participle gedafen becoming, fit, suitable. The æ here is apparently for umlaut ę before ft , st , which explains the two-fold Middle English development daft and deft . The primary meaning of the adj. must have been ‘becoming, fit’; compare the adv. gedæftlíce fitly, suitably, seasonably, and the vb. gedæftan to make fit or ready, to prepare; from ‘fit, ready, apt’ came the general later sense of deft ; from ‘becoming, decens ’ as said of persons, came that of ‘meek, mild, innocent’, and from ‘innocent, inoffensive’ apparently that of ‘irrational’ said of beasts, and of ‘silly, foolish, deficient in sense’ as said of persons: compare a common sense of ‘innocent’, and the sense-history of silly adj., n., and adv. See also deft adj.
daff n.1, ‘a fool,’ is found c1325; its relationship to daft is uncertain; if originally distinct, it may have contributed to the development of the sense ‘foolish’ here.
Daffy as an adjective meaning daft, simple has a first cite of 1884.
And who on earth knew that Daffy was once a slang term for gin?
Etymology: < the name of Thomas Daffy , an English clergyman of the seventeenth century.
Orig. in Daffy’s elixir, a medicine given to infants, ‘tinctura sennæ composita’ (Dunglison), to which gin was commonly added; hence, a slang name for gin itself.
Here’s the earliest cite in OED and the two most recent.
1680 The True News: or, Mercurius Anglicus no. 33 10–13 Mar. /2 Whereas divers Persons have lately exposed to sale a counterfeit Drink called Elixir Salutis, the true Drink of that Name, having been long since published by Mr. Anthony Daffy, (and generally known by the name of Daffy’s Elixir Salutis), [etc.].
1882 Punch 29 Apr. 193/2 A good many of them‥had been partaking freely of daffy.
1967 E. Burton Georgians at Home vi. 226 They [sc. Ward’s pills] could hardly have done more harm or good than the snake-root and brandy‥, Daffy’s Elixir, usquebaugh, [etc.].