There is a very useful website which I usea lot at Chambers Word Wixards. It has a dictionary and Thesaurus as well as helpwith missing words. Unfortunately it is not as complete as the printed dictionary, and I suspect the same may be true of software. Another annoying feature of the website is that you might select a word from the lists it gives you to complete a pattern (letters and question marks) then if you put that same word in their dictionary section for the meaning, it claims no knowledge of it.