WordWeb free version is the Master of free English dictionaries on the net, contains good Pronunciations and 150000 root words, and easy to use...
WordWeb is a one-click English thesaurus and dictionary for Windows that can look up words from in almost any program. It works off-line, but can also look up words in web references such as the Wikipedia encyclopedia. Features of the free version include:
Definitions and synonyms Proper nouns Related words Pronunciations
150 000 root words 120 000 synonym sets Look up words in almost any program