So ...

We are going to use a handy plugin called CM Tooltip Glossary.

Here it is:

https://wordpress.org/plugins/enhanced-tooltipglossary/

The plugin will allow you to ...

• easily create a glossary, encyclopedia or dictionary of your terms and show responsive tooltips when users hover over the terms
• check posts or pages for defined glossary terms, by adding links to a glossary term page that contains the definition of the term used
• display a tooltip containing the definition when users hover over the specific term
• create a responsive glossary index with all tooltip glossary terms used
• add unlimited tooltips to a site or within a glossary of terms

It's a small plugin (398 KB), but let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed ...

Now let's see how it works ...