With InfoPath Forms Services, you can take powerful InfoPath forms, and allow users to fill them out by using a browser. This enables your forms to reach more customers than ever before. Many Office users have been enjoying the convenience of spell check in Word and InfoPath. To enable this valuable feature for browser forms, we recommend pointing your customers to an Internet Explorer extension called ieSpell. It will check the spelling in your document, just like you would expect it to; you even get to store your personal word list or (clever!) point ieSpell to a Microsoft Office dictionary.
After filling out a form, hit the ieSpell button and it pops up a dialog, similar to the Microsoft Office spell check. If you want to know the meaning of the word, the thesaurus is just a click away.
If you are interested to learn more about ieSpell and other browser extensions, take a look at this article from the Internet Explorer team blog.