4643. sklerotes -- hardness
... obstinacy, perverseness. Cognate: 4643 -- hardness (literally, "hard from
being "), ie stubborn, obstinate. See 4642 (). Word Origin ...
/greek/4643.htm - 6kProverbs 16:22
Understanding is a wellspring of life to him that has it: but the instruction of fools is folly.
Topicalbible.org—AKJV

Isaiah 63:17
O LORD, why have you made us to err from your ways, and hardened our heart from your fear? Return for your servants' sake, the tribes of your inheritance.
Topicalbible.org—AKJV

Ezekiel 11:19
And I will give them one heart, and I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh:
Topicalbible.org—AKJV