A tribe is “gossa|ጎሳ” or “zer|ዘር”. But it means ethnic in the logical sense which is some steps more than a tribe. They are not interchangeable, but when many people say gossa it means ethnicity, that weird fact is it isn't. A gossa is something within a tribe. For example, I am an Ethiopian. My ethnicity is Guraghe|ጉራጌ, and my tribe is Yegoremar| የጎረማር. There are other more sections too, I have little knowledge about.