ἄθραυστος
From LSJ
ξένῳ δὲ σιγᾶν κρεῖττον ἢ κεκραγέναι → it's better for a stranger to keep silence than to shout (Menander)
English (LSJ)
ον,
A unbroken, E.Hec.17, IG2.1054d14, Melinnoap. Stob. 3.7.12; of persons, Plb.2.22.5; μέρος τῆς δυνάμεως D.S.19.30. Adv. -τως without breakage, κάμπτειν Gp.10.19.2, etc. 2 unbreakable, Arist.Mete.385a14; indestructible, ἄτομος Placit.1.3.18.