Plugin that links comments to keywords in the content

I have a 700 page website that has a series of reports. The reports contain similar terms that people may not understand so I would like to have a mouse over feature that explains that word every time it appears in my site. For example if the keyword is “John” and the comment is “John is the web developer” I would like a plugin that searches for the word John anywhere in the content and automatically applies the mouse over comment. Does anyone have any ideas of what plugin to use?

Thanks for your help in Advance