macOS 10.11 or later required.
Added: Dark Mode.
Support for macOS 10.15 Catalina.
Requires macOS 10.11 (or later).
Once extracted, drag Nisus Thesaurus to your Applications folder.
To enable the thesaurus inside other apps, including
Nisus Writer Pro or
Nisus Writer Express,
you may need to log out or restart your Mac.