“Internecine” is an unusual word, but not really all that obscure. It means “mutually destructive,” and it’s generally used in phrases like “internecine conflict” to describe something that affects to parties in conflict relatively equally. More recently it tends to be used specifically for contention between two groups who have something in common, such as two groups with different agendas in a single political party.
The word was first used in 1663 by Samuel Butler (there are at least two famous literary Samuel Butlers; this is the earlier one) in his poem Hudibras: “The Egyptians worshpp’d Dogs, and for Their Faith made internecine war.” Butler got “internecine” from the Latin phrase “internecinum bellum,” which meant “savage war of extermination.” That phrase came from “necare,” to kill, and “inter,” which is an intensifier that in this case makes the killing more thorough; complete extermination. Notice that “internecinum bellum” doesn’t carry any implication of mutuality. That additional meaning came about a century later, as a result of a major error!
What happened was that in 1755 Samuel Johnson (there are several famous Samuel Johnsons too) published the “Dictionary of the English Language,” which is generally regarded as the very first English dictionary, or at least the first one worth caring about. He included the word “internecine,, and that’s where the error came in. “Inter-” in most cases in English is a prefix that means “between” or “among”, but sometimes (one of those times being “internecine”) “inter-” is used as an intensifier. This confusion goes all the way back to the original Latin, by the way. Anyway, Johnson thought “inter-” meant “between” and defined “internecine” as “endeavoring mutual destruction.” Nearly every subsequent dictionary kept Johnson’s mistaken definition, and as a result “internecine” — which has always been a word uncommon enough that many people check a dictionary to make sure they’re using it correctly — actually came to mean what Johnson had written, without becoming redolent of error in the least.
Why “redolent”? Because that’s another word that’s changed meaning, although not because of a mistake. The literal meaning of “redolent” is “smells like.” It dates back to the 1400s and comes from the Latin “redolere” (emit odor). It originally signified a pleasant aroma, then the usage expanded to include unpleasant odors as well. More recently it tends to be used figuratively to describe things that don’t have smells at all, but are suggestive of something, as in “On every side Oxford is redolent of age and authority” (1856). It’s still used that way today — like, really today; just look one paragraph up.
