1. Culprit
There are several different accounts of the origin of culprit, but all of them seem to agree that the word was born out of a mistake. Back when French was still the language of the law in England in the Middle Ages (a hangover from the days of the Norman Conquest), the phrase Culpable, prest d’averrer nostre bille—literally “guilty, ready to prove our case”—was apparently the stock reply given by the Clerk of the Crown whenever a defendant gave a plea of not guilty. In the court records, this fairly long-winded phrase was often abbreviated just to cul. prit., and, as the Oxford English Dictionary explains, by “a fortuitous or ignorant running together of the two,” the word culprit was born.
2. Nickname
Nicknames were originally called eke names, with the verb eke used here in the sense of “to make longer” or “to provide an addition.” Sometime in the 13th century, however, “an eke-name” was mistakenly interpreted as “a neke-name,” and the n permanently jumped across from the indefinite article an to the verb eke. The same error—known linguistically as “rebracketing” or “junctural metanalysis”—is responsible for nadders, numpires, and naprons all losing their initial ns in the Middle English period.
3. Sneeze
Oddly, sneeze was spelled with an f and not an s, fneze, in Middle English, which gives weight to the theory that it was probably originally coined onomatopoeically. At least one explanation of why the letter changed suggests that this f inadvertently became an s sometime in the 15th century due to continual misreadings of the long lowercase f as the old-fashioned long s character, ſ.
4. Pea
Another word that developed from a plural-that-actually-wasn’t is pea. One pea was known as a pease in Middle English, but because of that final “s” sound, pease was quickly misinterpreted as a plural, giving rise to a misguided singular form, pea, in the 17th century. The actual plural of pease in Middle English, incidentally, was pesen.
5.Scandinavia
Scandinavia was originally called Scadinavia, without the first n, and is thought to take its name from an island, perhaps now part of the Swedish mainland, called Scadia. According to the OED, the extra n was added in error by the Roman scholar Pliny the Elder, and has remained in place ever since.
