GrayStud.io

Easy Glossary plugin helps you create a glossary of terms and definitions, automatically link terms in your content, display optional tooltips, and render an A–Z index. It includes a Settings page to customize behavior.

Easy Glossary

A lightweight, flexible glossary plugin that auto-links terms, shows tooltips, and provides an index shortcode.

techotronic

Adds tinytips tooltips to links on your site. Comes with 8 different themes. 
The tinytip can be added to a link using the WordPress visual editor.
The plugin can be automated to add the functionality for all links.
Tinytips tooltips are added for all links that have a “title” attribute.
See the <a href="http://www.techotronic.de/plugins/jquery-tinytips/" rel="nofollow ugc">plugin page</a> for demo pages.
For more information visit the <a href="https://wordpress.org/extend/plugins/jquery-tinytips/faq/" rel="ugc">FAQ</a>. 
If you have questions or problems, feel free to write an email to blog [at] techotronic.de or write an entry at <a href="https://wordpress.org/tags/jquery-tinytips?forum_id=10" rel="ugc">the jQuery Tinytips WordPress.org forum</a>
Localization
<ul>
<li>English (en_EN) by <a href="http://www.techotronic.de/" rel="nofollow ugc">Arne Franken</a></li>
<li>German (de_DE) by <a href="http://www.techotronic.de/" rel="nofollow ugc">Arne Franken</a></li>
</ul>
Includes <a href="http://plugins.jquery.com/project/tinytips" rel="nofollow ugc">Tinytips</a> 1.1 jQuery plugin from <a href="http://www.mikemerritt.me/" rel="nofollow ugc">Mike Merritt</a>. 
Tinytips is licensed as <a href="http://www.mikemerritt.me/plugins/tinyTips/license.txt" rel="nofollow ugc">free of charge for anyone</a>. 
jQuery Colorbox uses the jQuery library version 1.4.2 bundled with WordPress 3.0.

jQuery Tinytips

Adds tinytips tooltips to links on your site. Comes with different themes.

Easy Glossary vs jQuery Tinytips