I was going to title this post "words you only ever see written down"... but how else would you see words?
English has quite a few words. Indeed, English is a bit of a rogue language, lurking in darkened alleys until less hardened languages walk past, at which point it jumps them and steals all their words, engorging its dictionary on them to enhance its prodigious girth. Or something.
However, there are a lot of words that don't get used terribly often. And then there are those words that you encounter in print, indeed may encounter frequently in print, but never actually hear used. Which is always a little odd, especially when you come to a point where, actually, the best word to use is egregious. Or deleterious. Or whatever.
The problem then is this: how do you pronounce the word? I mean, as long as nobody around you knows the correct pronunciation, you're good, but if not then you stand a good chance of getting it wrong, even badly wrong. And it's not like there are any common rules for pronunciation - what with English nicking most of its words from other languages, "sounding it out" falls apart really quite quickly. (Unlike French, or Spanish, or any of the Romance languages, where once you've got the vowels down it becomes trivial. Except for "estadounidense".)
Fortunately, it appears I got 'bier' right. And 'eidolon', 'egregious', and 'deleterious'. However, I got 'facets' wrong the first time I used it, and likewise 'chitin'. So I guess I'll call that a draw.