The Collaborative International Dictionary of English v.0.48:

Dullard \Dull"ard\, n. [Dull + -ard.]
   A stupid person; a dunce. --Shak. -- a. Stupid. --Bp. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dullard
    n 1: a person who is not very bright; "The economy, stupid!"
         [syn: stupid, stupid person, stupe, dullard,
         dolt, pudding head, pudden-head, poor fish,
         pillock]
    2: a person who evokes boredom [syn: bore, dullard]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "dullard":
   Boeotian, block, clod, dimwit, dolt, donkey, dope, dullhead,
   dumb cluck, dumbbell, dummkopf, dummy, dunce, gowk, idiot,
   ignoramus, jobbernowl, lackwit, lamebrain, lightweight, looby,
   loon, moron, niais, nincompoop, ninny, ninnyhammer, nitwit, noddy,
   put, simpleton, stupid, thickwit, witling



The Devil's Dictionary (1881-1906):

DULLARD, n.  A member of the reigning dynasty in letters and life.
The Dullards came in with Adam, and being both numerous and sturdy
have overrun the habitable world.  The secret of their power is their
insensibility to blows; tickle them with a bludgeon and they laugh
with a platitude.  The Dullards came originally from Boeotia, whence
they were driven by stress of starvation, their dullness having
blighted the crops.  For some centuries they infested Philistia, and
many of them are called Philistines to this day.  In the turbulent
times of the Crusades they withdrew thence and gradually overspread
all Europe, occupying most of the high places in politics, art,
literature, science and theology.  Since a detachment of Dullards came
over with the Pilgrims in the _Mayflower_ and made a favorable report
of the country, their increase by birth, immigration, and conversion
has been rapid and steady.  According to the most trustworthy
statistics the number of adult Dullards in the United States is but
little short of thirty millions, including the statisticians.  The
intellectual centre of the race is somewhere about Peoria, Illinois,
but the New England Dullard is the most shockingly moral.