If you are looking for an easy way to set up a Glossary of Terms this is just the WordPress plugin to use.
The Explanatory Dictionary by Ruben Sargsyan allows you to explain terms both by using a Glossary and a Tooltip.
This is demonstrated on MyWordPress ,everything that is pink and italic will pop up a Tooltip and also has an entry in the Glossary.
To acheive the pop up Tooltip you must have an entry in the dictionary.
It is possible to limit the number of words that are referenced in each post and exclude portions of the post by use of the [no explanation][/no explanation] tags.
This is a very easy WordPress plugin to use and setup.