Meaning of hard-bitten

[Anchela]

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms - hard", question 8

The ......... dictator refused to grant clemency to his imprisoned political opponents.

(a) hard hearted
(b) hard pressed
(c) hard copy
(d) hard bitten

English Language Tests, Intermediate level

ESL/EFL Test #189 "Idioms - hard", answer 8

The hard hearted dictator refused to grant clemency to his imprisoned political opponents.

Correct answer: (a) hard hearted
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What does hard-bitten mean?
Thank you in advance.

Anchela

[Conchita]

hard-bitten adjective
If someone is hard-bitten, their character has been made stronger as a result of difficult experiences in the past and they control and do not show their emotions:

This particular murder case was so horrific that it shocked even the most hard-bitten of New York police officers.

(Cambridge Advanced Learner's Dictionary)

[Saneta]

hard hearted= hard-hearted?

thanks