While checking for misspelled words in a document, you probably click the Ignore Once or Ignore All button a few times. Doing so lets you skip a word that you don’t want to change but that the feature thinks might be misspelled. Spelling and Grammar remembers the words you skip and skips them during subsequent checks. Most of the time, that’s what you’ll want. Occasionally, it’s a problem. You might realize that the word was misspelled and you need to change it. Unfortunately, Spelling and Grammar won’t find ignored words, after the fact. 
You can scan the document visually, but that’s definitely a problem in a long document. You can use the Find feature, if you can remember the exact misspelling. The easiest and most efficient solution is to simply reset the Spelling and Grammar feature as follows:

  1. Execute the Spelling and Grammar feature as you normally would—press [F7] or choose Spelling and Grammar from the Tools menu. Check the Review tab in 2007 applications.
  2. Click the Options button.
  3. In the Proofing Tools section, click the Recheck Document button.
  4. Click Yes to confirm your choice.
  5. Click OK to return to the spell check task.

Spelling and Grammar will now identify all misspelled words, even words you said to ignore in the last session.