Actually, Nubian is an erroneous term from the 17th century referring to a tribe called the Noba, who were wrongly thought to have been the direct descendants of the Kushites and Aksumites, when in fact, there was no one people or tribe that composed these ancient Kingdoms.
The area south of Egypt was first called "Ethiopia" by the Greeks, a name that the Aksumites adopted later on, so, Ethiopia is was not originally the name of a Kingdom or country, but of a region that included the Kingdom of Kush, the modern country Sudan and Ethiopia.