Go to the Glossary in the left navigation, then edit page using 'source editing'.
Once there you can add a new line of content in the format:
;ABBR:full text of abbreviation [[[File:glossary list.jpg|thumb|500x500px]]] so it looks like this
- GIS
- Geographic Information Services
or
- GPS
- Global Positioning System
After that, any time the abbreviation is used on another page, it will automatically be applied with the full description as a hover link.
This will take half an hour or so to actually show up as it seems to search the pages and remember things!
