Wordist is an open source dictionary with incremental search hosted entirely on a static web server.
There's no backend logic doing anything fancy; it's just a big folder full of little javascipt snippets with corresponding definitions, parts of speech, etc. so you can experiment with language without 3rd-party APIs.
The entire dataset is a bit hefty to access directly (> 20MB), but breaking it up into little pages of words and definitions keeps it light-weight and speedy for the web. Big thanks to the GNU Collaborative International Dictionary of English for the data that makes Wordist possible.
See the source code on this page for examples on how to use Wordist in your own projects.
There's also a wordist searching game called circular dictionary — try to find words and get points by how often they occur in the dictionary!
Wordist is fully open source. You can read more, download, and fork this project on GitHub.