Terms and Definitions can be shown together when you choose the “Classic + Description” view on the “Glossary Index page” settings tab.
The definition that is shown underneath the term is the same definition which shows in the Tooltip, this means that it may be short and concise.
In case your term definitions are long – but you still want to show them in the Glossary Index Page, you can set the manual Excerpts and use the “Classic + Excerpts” view.