: cruel, hard-hearted.

What is a hard hearted person?

: lacking in sympathetic understanding : unfeeling, pitiless.

What are the two meanings of iron?

1 : of, relating to, or made of iron. 2 : resembling iron. 3a : strong and healthy : robust an iron constitution. b : inflexible, unrelenting iron determination. c : holding or binding fast an iron grip.