Next time you feel the urge to make your sparring partner aware of his lack of knowledge, soften the blow with one of these old-timey terms for ignorance.
This is one of many words that began with a literal meaning that shifted to the figurative. If a person was a lack-latin—or, to use the full insult, Sir John Lack-Latin—Latin was Greek to them. Back in the 1500s, that meant they were a bit of a dum-dum, so this word became a synonym for lackwit, numbskull, and doofus.
Anyone roaming around after dark is benighted in the literal sense, which has been around since at least the 1500s. By the following century, the meaning had broadened, as meanings tend to do. The figurative definition, courtesy of the Oxford English Dictionary, says someone who is benighted is “Involved in intellectual or moral darkness.” This use by the poet John Milton in 1637 is ominous: “He that hides a darke soule, and foule thoughts Benighted walks under the mid-day Sun.” An example from 1865 in the Pall Mall Gazette is more ignorance-centric: “Respectable old Russell Whigs, on whom charges of moral corruption operate much more powerfully than charges of intellectual benightedness.”
Speaking of light-out terms for ignorance, here’s one similar to unenlightened, blinded, and in the dark. Animals, who don’t follow human politics or sports with much enthusiasm, are thought of as ignorant in this sense, as seen in an OED example from 1914: “An animal life, a life unirradiated by hope or aspiration or sentiment or by the striving for beauty.”
Since the 1500s, this sad, sad word has been literal, meaning a place or person with no books. In our current electronic wonderland, literal booklessness has multiplied. But since the 1700s, bookless has also meant ignorant of books or not well-read.
This similar (and rare) word describes someone who is utterly lacking in lore—or, more specifically, knowledge, facts, data, info, etc. Loreless was spotted occasionally in the 1300s and rarely since. It turned up in 1836 in Tait's Edinburgh Magazine, in a description of “The poetry of his loreless soul.”
Not all ignorance is bad. Sometimes calling out a person for their lack of knowledge is complimentary, depending on who’s doing the calling: For example, a flatty is ignorant of the ways and means of criminality, especially being a thief. The term is apparently related to flatfoot, a word for a police officer; Green’s Dictionary of Slang records it as also meaning a clueless cop.
This variation of incognizant is rare but wonderful. It appeared in G.H. Taylor’s The Excursion of a Village Curate in 1827, in a sentence that doesn’t exactly show respect to an elder: “I pardon you, my choleric incognoscent octogenarian.”
Most words have origins that are vague at best, but not mumpsimus. According to the OED, this word came to be “apparently in allusion to the story (1516 in Erasmus) of an illiterate English priest, who when corrected for reading ‘quod ore mumpsimus’ in the Mass, replied, ‘I will not change my old mumpsimus for your new sumpsimus.’” So someone who is a mumpsimus isn't just ignorant; they're obstinately ignorant.
Ultracrepidarian types can be damned smart and quite knowledgeable about something. But they have a bad habit of blabbing about matters outside their area of expertise. As philologist Fitzedward Hall put it in an 1872 example: “His assumption of judicial assessorship, as a critic of English, is, therefore, to borrow a word from Hazlitt, altogether ultra-crepidarian.” In other words, he doesn’t know what he’s talking about.