λάθρῃ · lathrēi — LSJ
secretly, by stealth, ὁ δέ οἱ παρελέξατο λάθρῃ Il. 2.515; ἀνήρ, ὃς ἐμίσγετο λάθρῃ Od. 15.430; λάθρῃ κτείναντες treacherously, 17.80; ἀλλά τε λάθρῃ γυῖα βαρύνεται imperceptibly, Il. 19.165: in Trag. and Att., S. Aj. 1137, OT 386, Ar. Ra. 746, Th. 4.39, Pl. R. 347b, etc.
c. gen., λάθρῃ τινός unknown to one, λάθρῃ Λαομέδοντος Il. 5.269; λάθρῃ τῶν ἄλλων στρατηγῶν Hdt. 8.112, cf. 9.90, S. OT 787, OC 354, Ar. V. 347, X. An. 1.3.8.—Freq. written λάθρα, λάθρη in codd. and Pap., but λάθραι (i.e. λάθρᾳ) in UPZ 19.28 (ii B. C.) and in some of the best codd., as the Laurentian of Sophocles, also in POxy. 16 of Th. l.c. (i A. D.):—other forms are λάθρα, h.Cer. 240, E. Fr. 1132.28; λαθρηδόν, AP 7.202 (Anyt.); λαθρηδά, Luc. Cal. 21; λαθρηδίς, Hdn.Gr. 1.512 (-δως (sic), Cyr.)