твердый как железо

From LSJ

πατρὶς γάρ ἐστι πᾶσ' ἵν' ἂν πράττῃ τις εὖ → homeland is where life is good | homeland is where it is good | ubi bene, ibi patria

Source

Russian > Greek

σιδήρεος, σιδάρεος, σιδηροῦς