dull: [13] Dull originally meant ‘slow-witted’. It was borrowed from Middle Low German dul, a descendant of the prehistoric Germanic adjective *dulaz, which also produced German toll and Old English dol ‘stupid’ (the Old English adjective does not seem to have survived beyond the 10th century). The modern meaning ‘boring’ developed in the 15th century. The now littleused dullard [15] is a derivative (reflecting the adjective’s original sense), as also is probably dolt [16]. => dolt
