Remove item from database

I made new items and 1 item is not visible.
The item name is "Abstract" and it is not in the list of items in type elements.

However, when I want to make a new element with the name "Abstract", I get the message that it already exists in "Item Type Metadata" element set.
So I guess there this is a fault.

How can I search this in the database and delete it or what do I have to do ?

Omeka version is the latest.

It sounds like two different things are being mixed up, Items vs. Elements.

Elements are the metadata fields available for Items. Thus, an Item named "Abstract" will not appear in the list of elements.

The "Abstract" element might already be there if you are using the Dublin Core Extended plugin.

That's correct, I installed the Dublin Core Extended plugin.
Where can I find/see the Abstract element from Dublin Core Extended plugin ?