εἷς a neut. dat. (ἰῷ κίον ἤματι) also occurs in Il. The orig. form was prob. !ενς, cf. Lat. unus. The fem. μία points to a second Root, cf. οἶος with μόνος. one, Hom., etc.; εἷς οἶος, μία οἴη a single one, one alone, Hom.; εἷς μόνος Hdt. with a Sup., like Lat. unus omnium maxime, εἷς ἀνὴρ πλεῖστον πόνον παρασχών Aesch.; κάλλιστʼ ἀνὴρ εἷς Soph.; πάντων εἷς ἀνὴρ τῶν μεγίστων αἴτιος κακῶν Dem. in oppos., made emphatic by the Art., ὁ εἷς, ἡ μία Hom., Attic with a negat., εἷς οὐδείς nullus unus, no single man, Hdt., Thuc.; οὐχ εἷς, i. e. more than one, Aesch.; and more emphatic, οὐδὲ εἷς, μηδὲ εἷς, v. οὐδείς, μηδείς. εἷς ἕκαστος each one, each by himself, Lat. unusquisque, Hdt., Plat. often with κατά, καθʼ ἓν ἕκαστον each singly, piece by piece, Hdt., etc.; so, καθʼ ἕνα, καθʼ ἕν one by one, Plat. with other Preps., ἓν ἀνθʼ ἑνός above all, Plat.: —ἓν πρὸς ἕν, in comparisons, Hdt., Plat.; εἷς πρὸς ἕνα Dem.: —παρ’ ἕνα alternately, Luc. one, i. e. the same, εἷς καὶ ὅμοιος Plat.: c. dat. one with . . , Eur. one, as opp. to another; so, ὁ μὲν . . , εἷς δὲ . . , εἷς δʼ αὖ . . , Od.; εἷς μέν . . , ἕτερος δέ . . , Xen. indefinitely, εἷς τις, some one, Lat. unus aliquis, Soph., Plat.;—then alone, like our indef. Art. a, an, (as faber unus Hor.), Eur. οὐδὲ εἷς οὐδὲ δύο not one or two only, Dem.