Based on the 20-volume Oxford English Dictionary, the Shorter Oxford English Dictionary contains an incredible one-third of the coverage of the Oxford English Dictionary.

Features include:

-Over 600 000 words, phrases, and definitions
-80 000 quotations illustrating words in use throughout the centuries
-85 000 audio pronunciations
-100 000 etymologies
-Pattern search and spelling suggestions
-Full Text Search and Random Word

No internet connection is required, and you can use the OS X Services feature to look up selected words in most programs.