Whether it be online or hardcover or eBook or whatever, what is the best thesaurus to use for writing a fiction novel? Epic fantasy if that's necessary.
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I've tried both Merriam Webster and the OED and they both want you to sign up for either yearly or weekly subscription plans, which when I can either look at websites or the physical dictionaries I own isn't worth it for the convenience of being able to quickly look stuff up while writing. I went with both of those because I assumed they would have better quality control, but is there an option that is not a subscription service that is still a good dictionary and/or thesaurus?
http://www.wordnik.com seems to be the best online thesaurus, though one is presented with such a hailstorm of synonyms and near-synonyms and synonyms from divergent disciplines it can be rather overwhelming.
I've used it for several years, but recently found a thesaurus called "Artha" that sits on the desktop and is spectacularly well-designed. It's easy to find (just google "Artha thesaurus") and there are many places to download it from. I use it on Linux; hopefully it's available for other OS's.
I personally prefer a physical thesaurus for research... there's just a feel to it when crawling through topical sections I have not found online -- searching for a word online is just not the same as trolling through the sections and getting led along.
The 1911 version of Roget's Thesaurus is online and searchable. Being 100+ years old now, it could serve to provide the words you don't already know. I'd, of course, be careful about using antiquated words more likely to cause confusion than provide clariy.