I’ve long known that OS X’s Dictionary app could accept plugins but this is the first one that I’ve ever found that was worth installing.1
Terminology for OS X Dictionary, like Terminology for iOS, uses the WordNet lexical database. WordNet is a pseudo-dictionary/thesaurus that not only links word forms but specific phrases of words, making Terminology an excellent resource not just for the everyday user but especially for the writer.
Best of all, the OS X Dictionary plugin is free! If you find the plugin useful, be sure to support Agile Tortoise (the maintainer) by purchasing the iOS version.
There aren’t many to choose from in the first place; if you know of other dictionaries worth installing, please let me know! ↩