I received an email today from a woman asking about the word 'dunsicall'; she writes: "I found it in C.S. Lewis' That Hideous Strength. The portion of the sentance is "...utterly to be renounced and abominated as a galli-maufrey of papistry, gentilism, lewdness and dunsicall folly.""

it appears to be an early variant of the now rare 'duncical' - of or pertaining to a dunce; dull-witted, stupid, blockheaded.

all well and good, but this led me to the etymology of the word dunce (duns):

An application of the name of John Duns Scotus, the celebrated scholastic theologian, called ‘Doctor Subtilis’ the Subtle Doctor, who died in 1308. His works on theology, philosophy, and logic, were textbooks in the Universities, in which (as at Oxford) his followers, called Scotists, were a predominating Scholastic sect, until the 16th c., when the system was attacked with ridicule, first by the humanists, and then by the reformers, as a farrago of needless entities, and useless distinctions. The Dunsmen or Dunses, on their side, railed against the ‘new learning’, and the name Duns or Dunce, already synonymous with ‘cavilling sophist’ or ‘hair-splitter’, soon passed into the sense of ‘dull obstinate person impervious to the new learning’, and of ‘blockhead incapable of learning or scholarship’.[E.A.]

so it's a short step from 'hair-splitter' to 'blockhead'..