Well where in a state there's no word in a language to differentiate between a citizen and someone of a title ethnicity, i can call it an ethnostate. Say Armenian or Polish: there's no 2nd word in their languages for that. Because there are so few citizens who aren't of title ethnicity, and they are so marginalised and subject to such a quick assimilation, there isn't even a need to bother inventing a word.

If there is such a word say, "Kazakh" vs "Kazakhstani" or "Russkiye" vs "Rossiyane", existence of such a word shows that this state is an empire.

Sometimes the "ethnic" word simply doesn't exist, say in "Canadian" or "American" for U.S.: it's only citizenship, there's no ethnicity at all - neither the word nor substance - showing a "melting pot" country.