"Ethiopian" Is Already a Proper Noun

The word Ethiopian functions as both a proper adjective and a proper noun in English.

• Proper adjective: "Ethiopian coffee," "Ethiopian Airlines," "Ethiopian calendar."
• Proper noun (demonym): "She is an Ethiopian." "The Ethiopians have a rich history."

It derives from the proper noun Ethiopia (the country) + the suffix -an. Capitalization is always required.

No separate "proper noun form" exists—Ethiopian does double duty.