Just look at those words! Aren't they wonderful? And as readers who consume a wide variety of literature, we recognize them, don't we? Of course we do!
A more difficult question is "Do we know exactly what they mean?" For my part, I'm not ashamed to say "not exactly, no."
These sorts of words are what author Seth Stevenson calls "bubble vocabulary." In his 2014 Slate article Shibboleth. Casuistry. Recondite., he takes a look at these words at the very edges of our vocabularies and suggests some strategies for attempting to employ them.
Most of us are pretty skilled at getting the general gist of a word from context. We come to an understanding of the new string of letters by how it's used in a sentence and by the surrounding discussion in the work we're reading. However, most of us are reluctant to use these words ourselves because we're not confident in our understanding of all the nuances and because in many cases, we have no idea of how the word is pronounced.
As a fairly precocious reader, I had a large bubble vocabulary in my early teens. I remember that Frank Herbert's science fiction novel Dune introduced me to quiescent, which looked like "quiet" but also seemed to mean "still." Even more vexing was ecclesiastical, which I encountered in Harper Lee's To Kill a Mockingbird. I was pretty sure that it had something to do with religion, but my mental pronunciation of it was essentially "eckle-steckle" because I had never heard anyone use the word aloud.
Stevenson notes that pushing the limits of your vocabulary in a situation in which others will e judging you—such as a job interview—is not wise. He does, however, encourage his readers to be less self-conscious and to stretch their verbal wings in less fraught encounters—and to take any corrections with good humor. Likewise, when the shoe is on the other foot and your friend or colleague uses or pronounces a word incorrectly, he suggests that we provide the other speaker with tactful corrections.
For example, if at thirteen I had been brave enough to trot out my new To Kill a Mockingbird word by saying "Look at all those things on the altar. Now I know what Harper Lee meant by eckle-steckle impedimenta!" then my companion might respond, "Yes, it's an amazing collection of ecclesiastical bits and pieces" (using the correct pronunciation: əˌklēzēˈastək(ə)l or if you prefer, uh-KLEE-ZEE-a-stuh-kuhl). "Let’s all treat each other as friends," advises Stevenson: "Friends who are unafraid to stir some spice into the verbal soup."
I enjoyed this article a great deal, especially because I agree with Stevenson's evident love of language. "Juicy vocabulary words are a hoot," he says: "They are one of the great pleasures of conversation." I'm not going to argue with him!
Finally, most of us will be unable to resist an added feature in the column: The Slate Bubble Vocab Quiz. Your humble correspondent got 13 out of 18 correct. (Two years of high school Latin helped a great deal.) As an added incentive, the mysterious three words from the title are among the words in the quiz, so you can learn their meanings (if you don't know them already) without separate dive into a dictionary.