Word 2013 opens one dictionary per language when you define a word (Review > Define). If you downloaded more than one and the dictionary you want isn’t opening, you can switch dictionaries. The trick is to use Manage My Apps to control which dictionary is set to “visible” and to hide the others.
(Need to install a dictionary first? See Install a dictionary.)
Click Insert > Apps for Office.
Click My Apps > Manage My Apps.
Manage My Apps will open in a browser. If you’re prompted to, sign in.
For every dictionary you don’t want to use, under Action, click Hide.
If the dictionary you do want to use isn’t already in the list of visible apps, next to Show, click Hidden.
Then find the dictionary you want to use, and under Action, click Retrieve.
Back in Word, click Insert > Apps for Office.
If you don’t see the dictionary in the list of apps, click Refresh.
That dictionary will open whenever you define a word.
To learn more about apps for Office and what other apps are available for Word, see Get an app for Word.