When something is “pertinent,” it’s relevant. The heat-regulating system in your oven, for example, is pertinent to how well your cake comes out when you’re baking. The word is from the late 1300s (the Middle English era), and made its way to English via French. Its ultimate root is Latin: “pertinare,” which means the same thing, “to be relevant.”
“Impertinent,” however, does not mean “not relevant.” At least not nowadays. It also entered English at about the same time as “pertinent,” and originally it did mean irrelevant (“irrelevant,” by the way, uses its prefix sensibly and means precisely “not relevant”). But “impertinent” fairly quickly came to mean “not appropriate for a particular circumstance,” which is not quite the same thing. A citation from 1583 reads “Many ignorant practicioners … [have endeavored] to cure this infirmitie with many impertinent medicines.”
While the meaning of “pertinent” stayed pretty much the same, “impertinent” continued to drift. By the 1600s it was used to mean absurd, trivial, and silly. By the 1800s it tended to be used in relation to individual people and what they did, and generally meant “intrusive” or “rude.” “He thought the stranger’s tone rather impertinent” (1847). Today “impertinent” is still in use in that way, although it’s not as common as it once was. That’s probably because while impertinence was once generally frowned upon, fewer and fewer people seem to have any qualms about being rude or intrusive.
Since we’ve just accidentally stumbled across “qualm,” it’s a word with a pretty interesting (and not entirely understood) history. In spite of the word’s relative rarity nowadays, there have over the centuries been four different words in English that were all “qualm.” In the 1400s there was a “qualm” that was what you called the sound a raven makes. That “qualm” disappeared, probably after someone noticed that when ravens are making a noise it sounds a lot more like “caw” (or perhaps the ravens realized we were talking about them and changed their tune). In the 1500s there was a “qualm” that had to do with cooking. That “qualm” was a period of boiling in water, so you might “qualm” some vegetables. That version of “qualm” has also disappeared.
During that whole adventure with ravens and boiling water, there was an older word “qualm” around that had come from Old English, and meant widespread death and disaster such as a plague or a flood. That version of “qualm” is also obsolete now, but had the same root as the word “quell”, which today means to suppress, but originally meant “to kill.”
The only version of “qualm” that’s still in use appeared in the 1500s. It probably came from the same Germanic root words that the Old English “qualm” came from, but it’s quite a bit milder than a plague or widespread disaster. It means uneasiness or a moderate pain. There was an Old English word “cwealm” that had about the same meaning, and the current “qualm” is pretty likely an evolution of that word. It could, of course, be the same word as the disaster version of “qualm,” and the meaning just drifted over the centuries. But nobody really knows, and nobody is willing to make a definite claim either way. They probably have qualms about appearing too impertinent.
