Use the Thesaurus : Thesaurus « Documentation « Microsoft Office Word 2007 Tutorial

Select the text
Select the text
Click the Review tab. Then click the Thesaurus button.
Click the Review tab.
Click the list, then select a Thesaurus, if necessary.
Click the list arrow
Point to the word in the Research task pane. Click Insert to replace with the new word. Or Click Copy to copy the new word and then paste it within the document. Or click Look Up to look up the word for other options.
Point to the word in the Research task pane.

5.20.1.Use the ThesaurusUse the Thesaurus
5.20.2.Use the English AssistantUse the English Assistant
5.20.3.Translate Text Using the Translation ScreenTipTranslate Text Using the Translation ScreenTip
5.20.4.Turn off the Translation ScreenTipTurn off the Translation ScreenTip
5.20.5.Translate Text Using the Research PaneTranslate Text Using the Research Pane