Nicolas Bouliane

This plugin will display a small ??? icon that links to either the definition or the translation of the word. The plugin is a no-brainer to use: [define:dog] will define the word ?dog? and [en2fr:dog] will translate the word ?dog? from english to french. [wikies:dog] will show the Wikipedia article for the given word in spanish (es). Dictionary.com is used to define words, as it has definitions for technical terms too. Translation works with Google’s translation engine.
For a list of 2-letter language code, see here: http://reference.sitepoint.com/html/lang-codes

Word Definition Links

Inserts subtle links to definitions, Wiki articles and translations of words in multiple languages using short tags.

genkisan

<ul>
<li>easily switch on and off through Admin Options</li>
<li>display message without editing theme files (above 1st post or through widget)</li>
<li>display different message to different roles/users</li>
</ul>
Demo: 
<a href="http://ericulous.com/2007/03/09/genki_announcement/" rel="nofollow ugc">Plugin Details & Demo</a>

Word Definition Links vs Genki Announcement