HR definitions cannot be deleted if they are in use. Therefore you can check in the definitions list the definition usage:
Example of HR definition in use in Astrow Web
Click on the to see where it is used and then manually unlink the definition.
Checking HR definition usage in Astrow Web
In the example, the definition is used by employee Bruno Johns. Once you unlink it from the employee definition, you can delete the record. For more details please see HR Curriculum.
to see where it is used and then manually unlink the definition.