Moby Thesaurus is a free and open-source website for searching the largest thesaurus in the English language. The thesaurus itself has been around since the early 1990s, but until recently its content was only available on clickbaity websites with terrible interfaces and lots of banner ads. In 2014, I set out to change that by creating moby-thesaurus.org. The site is fast, contains no ads, works well on mobile, and is open-sourced on GithHub.
Moby works on mobile devices, too. Add it to your home screen for quick access.
npm install moby --global moby simple