Some dictionaries mark this word — meaning a superficial pretender to knowledge — as archaic, and indeed it may be so, since I can’t find a recent example from a printed work. And it was always in any case a scholarly or literary brickbat to throw at a rival, one hardly likely to appear in your daily newspaper.
A typical example appears in an article by Thomas Henry Huxley in the Fortnightly Review in 1878: “Judged strictly by the standard of his own time, Bacon’s ignorance of the progress which science had up to that time made is only to be equalled by his insolence toward men in comparison with whom he was the merest sciolist”.
The word, as you might guess from the spelling, comes from Latin. It derives from the verb scire, to know, which is also the root of other English words, like prescient, science, omniscient and conscience. The immediate Latin original was the diminutive sciolus, a person who had only a smattering of knowledge.
The related noun is sciolism, the practice of giving one’s opinions on subjects of which one has only superficial knowledge. That is a little more common, but the only recent example I’ve turned up was written by the American author and playwright Herb Greer in the National Review in 1998: “Tynan’s awful political sciolism sparks out now and again, but not offensively”.
Store it in the back of your mind — you never know when it might come in handy, simultaneously showing your own word power and your opinion of your opponent. By the time he has found a sufficiently large dictionary to discover you’ve insulted him, you can be well away.