ξένῳ δὲ σιγᾶν κρεῖττον ἢ κεκραγέναι → it's better for a stranger to keep silence than to shout (Menander)
ἀκραγής, σιωπηλός, ἀκέων, σιγαλός, σιγηλός, ἥσυχος