The Collins English Dictionary Complete & Unabridged and the Collins Thesaurus of the English Language in a software bundle offering a complete language and reference solution for writing, for work, for study, because you want to express yourself well, or just for the love of words.
Best Dictionary/Thesaurus — For US$39.99 you can have the ultimate language reference. over 500,000 English words and 377,000 synonyms with key expressions, examples sentences, culture, and usage notes. You can d/l the whole thing and use it offline. It's expensive, but it's all you'd ever need.