You can very easy to enable Glossary system on your site with Glossary plugin.
The concept is very simple. You create section and name it Glossary. You create type _Glossary Definition and and at least one field there which will contain description. It may be textarea or even HTML field. Add some definitions into section.
Now configure Glossary plugin and set source section and type you have just created. Do not forget to publish it.
Article titles will act ad definition. Now plugin will be triggered
onPrepareContent() even all across Joomla. And replace text that conform to definitions to links or tooltips.
If it does not work in some extension, then it means that text generated by this extension do not trigger
onPrepareContent even. You can contact developer of that extensions and ask to add
<?php $text = JHTML::_('content.prepare', $text); ?> for all texts displayed.