This word meaning a stupid person is an eponym for John Duns Scotus (c.1265-1308), a leading scholar of philosophy and theology. Scotus was born in Duns, Scotland and his writings formed the philosophical core for a Scholastic sect named after him, the Scotists. In the 16th century, humanists and reformers began attacking the Scotists for splitting hairs and engaging in useless philosophical discussions. In retaliation, the Scotists railed against the new learning of the Renaissance. As a result, Duns’s followers became associated with those who refused to learn. As William Tindale put it in 1530 in An Answere Unto Sir Thomas Mores Dialoge:
Remember ye not how [...] the old barkyng curres, Dunces disciples and lyke draffe called Scotistes, the children of darknesse, raged in euery pulpit agaynst Greke Latin and Hebrue.
The sense meaning an idiot dates to at least 1579. From John Lyly’s Euphues, The Anatomy of Wyt from that year:
If one be hard in conceiuing, they pronounce him a dowlt: if giuen to studie, they proclaime him a dunce.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2016, by David Wilton