Genos and Eidos in Plato

English translates ‘genos’ as kind and ‘eidos’ as form, which differ in meaning as much as ‘herd’ and ‘brand’ do. But there are hard passages where ‘genos’ and ‘eidos’ have appeared to be synonyms, usually given the new meaning class. We show that, although ‘genos’ and ‘eidos’ are never synonyms and continue to mean kind and form, the word ‘eidos’ can be used figuratively, as a metonym, for a genos.