Definition: being a dunderhead
What is a dunder, and why do we use this word to insult people in a somewhat mild fashion? Alas, this is but one more unknowable in a long line of things that etymology has not yet figured out. It may come from the Dutch word for “thunder” (donder), but no one is sure about that. What we are sure about is that there are a great number of words for “stupid” or “stupid person” ending in -headed or head. A partial list includes the following: airhead, beefheaded, beetleheaded, blockhead, bonehead, bullhead, bubblehead, buffle-headed, butthead, chucklehead, deadhead, fathead, flathead, hammerhead, heavy-headed, idleheaded, ironhead, jolt-headed, jughead, knucklehead, loggerheaded, lunkhead, meathead, muddlehead, pinhead, pinheaded, ramhead, saphead, sheepheaded, sheepshead, thickhead, and wooden-headed.
Thus I pass away the time, and this lulls me on to drudge on the end of the Chapter with this Dunderheaded Master of mine, who to my knowledge is more a Madman than a Knight.
— Miguel de Cervantes, Don Quixote (anon. trans.), 1703
Definition: stupid, silly
Here we have a lovely example of a word which began its life (in our language, at least) with a figurative meaning, and only took on a literal one after more than a century of use. Anserine comes from the Latin anser, meaning "goose." The word is indeed used on occasion to mean "resembling a goose," but the 'silly as a goose' sense preceded this by a considerable length of time.
I am not of such anserin stupidity, but that I could make as ignominions at reorsion upon my adversary.
— John Menzies, Roma Mendax, 1675
Definition: a stupid, slow-witted, or obtuse person
The original meaning of blinkard was “one that blinks with or as if with weak eyes,” which soon added the pejorative meaning listed above. If you are a person who blinks often please accept our apologies for the English language, which can on occasion be needlessly cruel.
Poore foolish Blinkard, Beads-man vnto Christ,
For restitution of long lacked sight,
I maruaile what they fancie so inticte,
To be desirous of this lothsome light?
— Samuel Nicholson, Acolastus his After-witte, 1600
Definition: complete or utter ignorance
I haue compleyned before of the ignorance of Greik, & Latine tounges, the Ignoration whereof, no doute, hes moued vs a great part of this busines, specialie hauing to do with men that vnderstandeth not the proprietie of them.
— George Hay, The Confutation of the Abbote of Crosraguels Masse, 1563
Definition: stupid and confused, mixed up, or eccentric
The pate portion of addlepated comes from an older word for "head," in use since Middle English, and of uncertain origin. The addle portion may be traced back to the Old English word adela, meaning “filth, filthy or foul-smelling place.” As an adjective addle first had the meaning of “foul smelling and putrid” (specifically said of an egg), and later came to mean “confused or muddled.”
Those who belong to Madam Luna, as Hawkers of Almanacks and Pamphlets, Huntsmen, Ostridge-Catchers, Falkoners, Couriers, Salt-carriers, Lunaticks, Maggotty Fools, Crackbrain'd Coxcombs, Addle|pated Frantic Wights, Giddy Whimsical Foplings, Exchange-Brokers, Post-boys, Footboys, Tennis Court-keepers-Boys, Glassmongers, Light-horse, Watermen, Mariners, Messengers, Rakers and Glea|ners, will not long stay in a place this year.
— François Rabelais, The Fifth Book of the Works of Francis Rabelis (trans. by P. M.), 1694
Definition: exhibiting or characterized by nescience: ignorant, agnostic
Nescient, science, and omniscient (“having infinite awareness, understanding, and insight”) all share a root: each comes in part from the Latin word scire, meaning “to know.” Nescience, then, is "lack of knowledge or awareness."
True it is that he offends more hainously, that sins through knowledge, then he that slips through Ignorance: but we may not therefore flie to Ignorance for an excuse: for 'tis one thing to be [H] nescient, ano|ther to be wilfully Ignorant.
— Robert Dyer, The Christian's Theorico-Practicon, 1633
Definition: an act of foolishness or stupidity
Bêtise came to English from the French word bête, which has the meaning in that language of "idiot," or, more literally, "beast" (the literal meaning of bête is the one found in the term bête noire). In addition to an act of stupidity, bêtise may refer to stupidity or ignorance in general.
"I assure you," said she "I was only tormenting you a little, and you must own you deserve that; but you can't suppose I meant half what I said; that is a bêtise I can't conceive you guilty of.”
— Susan Ferrier, Marriage 1818
Definition: slow of mind : obtuse
Okay, fine. Why try to improve on a classic?
MORE TO EXPLORE: Nincompoop and Other Old-Fashioned Words for Stupid