φιλόφωνον

From LSJ

γελᾷ δ' ὁ μωρός, κἄν τι μὴ γέλοιον ᾖ → the fool laughs even when there's nothing to laugh at

Source

Russian (Dvoretsky)

φιλόφωνον: τό шумливость, болтливость Plut.