On a couple of occasions I've heard writers say that using a thesaurus is not a good idea. The argument was that if a word isn't part of your natural usage vocabulary, it will come out sounding wrong in context.
That is always a possibility, but it does assume that you don't have a lot of flexibility in your writing voice. I could make an argument that on the contrary, it's better to go for the right word, and if necessary, get help integrating it into the voice later.
I was thinking about this topic while I was recently watching Avatar: Legend of Korra with my kids. They use a lot of technologies that parallel technologies of our world, but they don't use the words for them that we would use. In particular, the character Bolin becomes a movie star. The problem with calling them "movies" would be that it might pull viewers out of the environment with too strong a reference to our own world and its technologies. Therefore, the show uses the word "mover" instead. Same idea, different word, different associations.
In our own world, we use different words for the same thing. Think, for example, about when you might expect to see or use the following words:
Can you imagine yourself saying, "Did you like that motion picture?" I can't. I'm more likely to ask, "Did you like that movie?" or possibly "What did you think of that film?" Motion picture seems to be something used exclusively by studios to describe their products: "A major motion picture." The more familiar and colloquial shortening "movie" has become the default word for this thing. "Film" refers to the material that movies were originally recorded to, and has a slightly different feel.
That different feel issue is right at the heart of this question of naming things. Sometimes you can feel happy going with your gut on what the word for something in your world should be. Sometimes not. An etymological dictionary can help you to delve into the "feel" behind the word and see if you can get more of a sense to it. A thesaurus can help you to see what other options might be out there with very different connotations.
I often use generic words when I'm in fantasy or science fictional settings. Generic words are words we have heard so many times in so many different contexts that we don't immediately associate them with one specific context. They can be very useful, because that lack of immediate context can allow an author to create their own associations within the story world. There are other instances, however, when the right word, with the right connotations, is out there and your story world would benefit immensely from having it appear in the right spot.
One of the words that I spent a long time looking for was the word "indulgence." It's not a word I use a lot in my own life, but it's really really useful for my Varin world, particularly when I am working with servant-caste characters. I remember writing along in my servant-caste character Aloran and feeling that word hovering out there at the edge of my consciousness. I would think to myself, "There's a word he would use to show how he understands the way that nobles express kindness to him, but I just can't think of it." In that case, I didn't use a thesaurus - one day as I was revising, the word finally just popped into my head. I was pleased, because I could go back through at that point and put it in the places where I'd been gesturing vaguely at that same idea without having the proper word for it. It probably would have been sensible of me to spend a bit of time with a thesaurus seeing if I could run across the word in a more systematic way!
What words do you need in your world? Is there one waiting out there for you that might have just the right social connotations to give your world extra dimension?
It's something to think about - and don't be afraid to use your references!