Did you know that word 'daft' derives from the Anglo-Saxon word 'Schmuck?". It actually means Schmuckers, as in "why don't you daft-off Norm".
Sorry Hill........ but.....
Although today we use "daft" to mean "crazy" or "foolish," it derives from the Old English "gedaefte," which meant "mild, gentle or meek." A "daft" person, when the term first appeared in Middle English as "daffte" around 1200, was simply quiet and humble, not noticeably nuts.
Unfortunately, while the meek may inherit the earth (or what's left of it, anyway), being humble does not always engender respect, and by 1325, "daft" was being used to mean "stupid," first in reference to animals, but soon in regard to people. Worse yet, by the early 16th century, "daft" had mutated into a synonym for "insane," which is where it rests today. If there's a silver lining to the story of "daft," it is that the word is today a rather gentle synonym for "crazy," more often used to mean "silly" or "impractical" than "seriously nuts."
I would hazard a guess that your use of the term "daft as a brush" means that you are either British or have spent time in the UK (but please don't ask me why "a brush," because I haven't the vaguest). "Daft" isn't in common use here in the US, but a probable relative is -- "daffy," which first appeared in the noun form "daff" back in the 14th century meaning "fool."
A more surprising "daft" relative is "deft," nearly the opposite of our modern "daft." Derived from the same Old English "gedaefte," "deft" separated from "daft" in the 15th century, and developed the "gentle" sense into its modern meaning of "skillful or subtle."