The English language has more words in it than I personally think is necessary. The vocabulary is so big, experts can only guess at how many words there actually are. That's because language is a changing thing, something that's always evolving. You can actually force some of those changes yourself. You just need to know how to make a word.
The Right Words
I'm not a big fan of inventing words, because like I said the language is already too big, but if you're going to do it you may want to try using a formula. There's a really easy way to invent new words, and people have been using it for years. Just add -ish.
How else would the word sheepish exist, if this trick didn't work? I was taking a picture of someone, once, and I told them to look look sheepish. It's one of those words you find in books all the time, sheepish, and even as I gave the direction I realized I don't really know what the word means. Timid, maybe? Bashful? I don't know; I've never really been around a living sheep.
I have, however, been around a book. So I might use the word bookish to describe someone, another simple word. If you need to convey a simple concept and you can't find an adjective that will do, just add -ish, and invent your own word.