It seems that it's possible to isolate a single glossary entry via a URL.
The only way I've found to trigger this is:
Edit an entry
Click save or cancel
The page that you are returned to looks like "/mod/glossary/view.php?id=xx&mode=entry&hook=xx" where "id" appears to be the course id and "hook" appears to be the id of the glossary item.
When sharing this URL to an unauthorised user they are, of course, re-directed to the login page. Once authorised they are re-directed to "/mod/glossary/view.php?id=xx&mode=entry" which brings them to the glossary, but looses the "hook" value, thus showing a blank glossary until they start to navigate manually.
Does anyone know of a better way to link directly to a glossary entry?