A warning
branch is not fully merged
appears when the branch you are trying to delete is not merged into another. This warning saves you from deleting a branch and its changes before you merge them so that you do not lose your changes.
In your case, it looks like you did not have a โmasterโ branch on your computer, since you received a message
* [**new branch**] master -> master
So, when you downloaded the master branch, where in dev , and then you tried git branch -d master , but since it was not merged from the point of view of dev, you got a message
With gitk --all you can see the whole tree, and there you will see how the master of the branch does not merge into another. Hence the message.
If you still want to remove it, just use the -D command
source share