Right now we are developing a module to add definitions to a Drupal site: Through the backend you can add words and synonyms together with descriptions of the words.
It works as a input filter, the words from the list will get a span and a dotted border-bottom. When hovering over the word, de description appears in a tooltip (qtip).
When ready the module will be announced at http://communiceerjekerk.nl and also contributed at drupal.org.
There are kind of similar modules, but not with the exact desired functionality. AND not for Drupal 7. (this module will only be developed for D7)
The idea behind the module is to explain the sometimes 'internal' language of the church (what has to be avoided, but this is not always possible) for the people who do not have knowledge about the church nor do know God.