On an test website with Joomla! 2.5.11, SEF and few other plugins I first installed "Glossary 2.8".
It works, but I did not like it. So I disabled it for the moment, looked for an alternative.
I tried Gnosis, started with version 1.0.9.
In the administrator interface I went to the component menu, had the Gnosis line with two (1.09: not quite correct) menu items.
Both menu items gave white screens only when clicked.
Thus I installed 1.0.b7 and later 1.0.6; these two had the correct menu items, but did not give anything better, just white screens.
Before each install I tried to remove all of Gnosis; Gnosis Package cannot be removed in the extension manager, it gives an error message like "manifest file cannot be found".
Furthermore I spotted a typo (compnetn instead of component), not important, see screenshot.