Words have always fascinated me. When I was young, I used to read the dictionary when I'd read all the books in the house at least twice. Since I've turned my hand to turning the words that fascinate me into stories I've learned one thing and that is not to use too many unfamiliar words for that will turn people off if the unfamiliar are strung in rows. The trick is to use one of the different words in a way that people can understand the meaning. Then I began writing fantasy. And here unfamiliar words can be a plus. There are two books I use frequently in my stories, and not only for having new words but sometimes for names.
The first book is a Seven Language Dictionary that goes from say French to English and English to french. There is Italian, German, Russian, Hebrew, Portuguese and Spanish. Here I might find a word I can use for horse but one that makes people understand the creature I'm describing. I came upon lobo for wolf. This book also has a section of Proper names and one of Geographical names. Great when you are using a character from another land or wanting to name your characters and perhaps using a geographical name for a last name. My only problem is getting lost in exploring and forgetting what I am looking for. Also in the print for soon I will have to use a magnifying glass.
The second book is The concise Dictionary of English Etymology. What fun this is when building a world that's foreign to the one we live in. Here one can find ways to spell a word that still makes it seem familiar to the reader. Take Amber, the Middle English word was aumbre in French ambre and in spanish Ambar amd Arabic anbar. Actually the word went from French to Spanish to Arabic and was called amber for its resemblance to ambergris.which is really a different substance. But if I used any of the three spellings in a fantasy, especially when describing a gemstone. people would know that is amber.
So look up these books especially when you're writing fantasy or if you have someone from a foreign land in your stories.