σής
From LSJ
ποταμῷ γὰρ οὐκ ἔστιν ἐμβῆναι δὶς τῷ αὐτῷ → it is impossible to step twice in the same river, you cannot step twice into the same rivers
English (LSJ)
ὁ, gen. σεός (as if fr. σεύς, which is given as nom. by Choerob. in Theod.1p.406H.); pl., nom. σέες Moer.p.339 P.; gen.
A σέων Hermipp. 94, Ar.Lys.730, Ph.2.461 (not σεῶν, v. Choerob. l. c.); acc. σέας Luc.Ind.1:—the forms σητός, σῆτες, σητῶν, etc., were later, as in Men.540.5, Arist.HA557b3, Thphr.HP9.11.11, Ph.2.361 (and v.l. in 2.461), cf. Moer. l.c., etc.:—moth, [χρυσὸν] οὐ σ. οὐδὲ κὶς δάπτει Pi.Fr.222, cf. Ar. l. c., Str.13.1.54, Ev.Matt.6.19, Ev.Luc.12.33; attacking books, Luc. l. c. 2 metaph., σῆτες ἀκανθοβάται or -λόγοι, of the Grammarians, bookworms, AP11.322 (Antiphan.), 347 (Phil.).