The iThesaurus app is a comprehensive thesaurus that'll help you reference words. Whether your kids need help with their homework or you need help sourcing a word for an email/document, iThesaurus will help you out.
It's simple to use, you type a word into the search box and it brings back a list of results (the app has access to over 140,000)
Within the results are relevant words that can be clicked to find out the meaning and also access an audible pronunciation (these audio pronunciations can be slightly odd sounding)
You can share words by email or through one of the popular social networking sites.
The iThesaurus app is an excellent educational app and will ensure you're never short of expressing yourself. Oh, and did I mention, it's completely free!