daft adj.

"simple, wanting in intelligence," also "crazy, mad," 1884, perhaps from daft (adj.), or from obsolete daffe "a halfwit" (early 14c.; mid-13c. as a surname), which survived in 19c. in dialects, itself of uncertain origin (OED finds a proposed origin in Scandinavian words for "deaf, stupid," such as Old Norse daufr, "phonetically inadmissible"). Compare late 15c. daffish "dull-witted, spiritless." With -y (2). Related: Daffily; daffiness. The Warner Bros. cartoon character Daffy Duck debuted in 1937.

late 13c., "foolish, ignorant, frivolous, senseless," from Old French nice (12c.) "careless, clumsy; weak; poor, needy; simple, stupid, silly, foolish," from Latin nescius "ignorant, unaware," literally "not-knowing," from ne- "not" (from PIE root *ne- "not") + stem of scire "to know" (see science). "The sense development has been extraordinary, even for an adj." [Weekley] — from "timid, faint-hearted" (pre-1300); to "fussy, fastidious" (late 14c.); to "dainty, delicate" (c. 1400); to "precise, careful" (1500s, preserved in such terms as a nice distinction and nice and early); to "agreeable, delightful" (1769); to "kind, thoughtful" (1830).

In many examples from the 16th and 17th centuries it is difficult to say in what particular sense the writer intended it to be taken. [OED]

By 1926, it was said to be "too great a favorite with the ladies, who have charmed out of it all its individuality and converted it into a mere diffuser of vague and mild agreeableness." [Fowler]

"I am sure," cried Catherine, "I did not mean to say anything wrong; but it is a nice book, and why should I not call it so?" "Very true," said Henry, "and this is a very nice day, and we are taking a very nice walk; and you are two very nice young ladies. Oh! It is a very nice word indeed! It does for everything." [Jane Austen, "Northanger Abbey," 1803]

For sense evolution, compare fond, innocent, lewd, also silly, simple.