Dunce is commonly used to mean a dimwitted person, but was originally a much more specific insult.
John Duns Scotus (c. 1265-1308) was a celebrated theologian, and his works on theology, philosophy, and logic were standard texts for 300 years after his death. Eventually, humanist and reformer philosophies started to push out the traditional Scotists, and these groups started to use the terms 'Dunsmen' and 'Dunses' (c. 1530) as a derisive alternative to Scotist.
The Scotists were criticised for hairsplitting, proposing needless entities and useless distinctions. The OED defined the original meaning of dunce as "'cavilling sophist' or 'hair-splitter'". This later devolved into "dull or obstinate person" and "one whose study of books has left him dull and stupid, or imparted no liberal education" (1579). Finally, the insult degraded to its current form, a "blockhead incapable of learning or scholarship" (c. 1580-90, gaining popularity through the 1600s).
Brevity Quest 2016