Parses posts for defined glossary terms and adds links to the static glossary page containing the definition. The plugin also creates a tooltip containing the definition which is displayed when users mouseover the term. Based on <a href="https://wordpress.org/extend/plugins/automatic-glossary/" rel="ugc">automatic-glossary</a>.
The code has been optimised from automatic-glossary and unnecessary code has been stripped to keep the plugin lean. However, support for php 4 has been removed and if you are looking for a php 4 glossary, please do download automatic-glossary (although I believe there is a little extra tweaking required).
The tooltip is created with JavaScript based on the article written by <a href="http://www.leigeber.com/author/michael/" rel="nofollow ugc">Michael Leigeber</a> <a href="http://sixrevisions.com/tutorials/javascript_tutorial/create_lightweight_javascript_tooltip/" rel="nofollow ugc">here</a> and can be customized and styled through the tooltip.css and tooltip.js files.
Users of WordPress versions less than 3.0 should use version 1.1 of this plugin.

TooltipGlossary

Parses posts for defined glossary terms and adds links to the static glossary page containing the definition and a tooltip with the definition.

Sabbir Noyon

Smart Dictionary Lookup enhances your WordPress site by providing quick, beautiful word definitions in a customizable popup when users double-click any word on the page.
Features:
✔ Fetches definitions from a free, reliable dictionary API 
✔ Stylish popup with Light/Dark mode options 
✔ Customizable popup position (Top/Bottom, Left/Right) 
✔ Admin settings page for easy configuration 
✔ Option to enable/disable the popup 
✔ Clean, minimal UI inspired by modern toast designs 
✔ Lightweight and conflict-free
Perfect for blogs, educational websites, content platforms, or any site where enhancing word understanding matters.
<h3>License</h3>
This plugin is licensed under the GPLv2 or later.

Smart Dictionary Lookup

Smart, instant word definitions with a beautiful popup when users double-click text. Fully customizable, lightweight, and WordPress-friendly.

TooltipGlossary vs Smart Dictionary Lookup