Create Relationships to Entity Particles from Custom Metadata Types
Where: This change applies to Lightning Experience and Salesforce Classic in Professional, Enterprise, Performance, Unlimited, Developer, and Database.com editions. Professional Edition orgs can create, edit, and delete custom metadata records only from types in installed packages.
How: To create a custom metadata relationship to an entity particle, first create an entity definition relationship field, then create an entity particle relationship field.
Now when you create a record for the custom metadata type, you can drill down and select a compound element for the relationship. For example, you can select Zip/Postal Code or Time Zone, which are compound elements of Address.