hard, harden, harder, hardness

Definition:

The term “hard” generally refers to something that is persistent, or unyielding.

The use of “hard” (in various forms) with “heart” refers to people being stubbornly unrepentant or disobedient (usually) to God.

The term “hard” could also be translated as “rebellious” or “stubborn” or “obstinate” or “unyielding” depending on the context.
The terms “hardness” or “hardness of heart” or “hard heart” could be translated as “stubbornness” or “persistent rebellion” or “rebellious attitude” or “stubborn disobedience” or “stubbornly not repenting.”
The phrase “hard of neck” could also be translated as “obstinate” or “rebellious”
The term “hardened” could also be translated as “stubbornly unrepentant” or “refusing to obey.”
“Do not harden your heart” could be translated as “do not refuse to repent” or “do not stubbornly keep disobeying.”
Other ways to translate “hard-headed” or “hard-hearted” could include “stubbornly disobedient” or “continuing to disobey” or “refusing to repent” or “always rebelling.”