Hi Emerson,
There is no such thing as a "global glossary" in Moodle. I suppose you mean a "Main Glossary"? Anyway, Main or Secondary glossaries are only available in the courses where they reside. If you want to show random glossary entries on your Moodle front page you'll have to create a glossary on the front page, to select random entries from.
Joseph
Edited by JR
Sorry about the confusion in my post, Emerson. Here is the correct information (hopefully).
In any Moodle course (and on the front page as well) you can have glossaries which can be Main, Secondary and optionally Global. The only Help is somewhat useful to understand this rather confusing terminology. Anyway, here goes.
If you create a Glossary in any course (or on your Moodle site front page) and you tick the Global box in the settings, then that "Global Glossary" will be available everywhere on your Moodle site (on the site front page and in each of the site's courses). Please note that you have to be logged in as Admin to be able to tick that box. "Available" means that any piece of text - anywhere on your site - which contains a word that is an entry in that "Global Glossary" will have that word automatically linked to that glossary.
Unfortunately, and that was your initial problem, a Global Glossary is only available to the Random Glossary entry block in the course where it resides and where the Random Glosssary block resides as well. That is a bug feature of Moodle.
To create your Random Glosssary block on your site's front page, follow Jon's advice, and create a glossary on your front page (it does not need to be set to Global if you only want to use it for the Random block feature).
Hope this helps,
Joseph