πλαστῶς

From LSJ

ᾁδειν ἀμουσότερα Λειβηθρίων → sing worse than Leibethrans, sing worse than the people of Leibethra

Source

Russian (Dvoretsky)

πλαστῶς: вымышленно, облыжно (μὴ π., ἀλλ᾽ ὄντως Plat.).