Yesterday, Greg Pierce (the dev behind Agile Tortoise) officially released an OS X Dictionary version of the Terminology database. It’s free, and it plugs directly into the built-in Dictionary app, meaning its definitions are available with a quick three-finger tap (and “Look up…” services) in any app on recent OS X versions.
You can download the dictionary and find installation instructions at the Agile Tortoise website. Be sure to complete the installation by enabling the new dictionary in Dictionary.app preferences.
If you haven’t already grabbed Terminology for iOS, doing so would be a great way to thank Greg for this excellent free resource!