https://www.powerthesaurus.org/ is a crowd sourced thesaurus where users can add and vote on synonyms for different words or phrases. It's phenomenal for coming up with words for different actions, perks, rules, or events.

Vocabulary is important to all writing, but in RPGs, you may have to select dozens or even hundreds of words that need to be descriptive, accurate, and evocative, and for that you need a thesaurus.

Power Thesaurus is a bit messier than other options, like https://www.thesaurus.com, but that often makes it more helpful for writing and design, in my experience.

For starters, Power Thesaurus has phrases. Say you have a perk and all you can think to call it is "get back up", but you want to see if you prefer a single word over the phrase. "Get back up" actually returns results, and by clicking through those results you can work toward some decent synonyms.

Power Thesaurus also provides "synonyms" that are barely synonyms, if you're willing to scroll far enough. On other thesaurus's (thesauri?) you only get "correct" synonyms, whereas here, you get everything that anyone could think of. This is great for when you actually know your word isn't right, but it's the closest you could come up with.

I use it all the time, for both general writing and when writing my RPG, and I firmly believe everyone here should as well.