μάρτυρος
From LSJ
Menander, Monostichoi, 483
English (LSJ)
ὁ, Ep. form for
A μάρτυς, ἐστὲ μάρτυροι Il. 2.302, etc.; also in Central Greece, IG9(1).226 (Drymaea), 364 (Naupactus), GDI 1684, al. (Delph.), etc.: sg. once in Od., οἷσιν ἄρα Ζεὺς μάρτυρος 16.423, cf. PGen.54.6 (iv A.D.). (Zenod. rejected this form, but it is defended in Sch. Il.Oxy.1087.22.)