Late 19th century. From post-classical Latin prothysteron or its etymon Greek πρωθύστερον, in scholia (medieval Greek or earlier) on Euripides Phoenissae 887, use as noun of neuter ofπρωθύστερος last first, in scholia (medieval Greek or earlier) on Euripides Orestes 702 from ancient Greek πρωτο- + ὕστερος later.