An example of implacable is a screaming child who won't listen to reason.
Implacable foes; implacable suspicion.
From this time she was the ardent champion of her husband's and son's rights; to her energy the cause of Lancaster owed its endurance, but her implacable spirit contributed to its failure.
When Louis the Lame died in 1445 his father came into the power of his implacable enemy, Henry of Bavaria-Landshut, and died in prison in 1447.
Frederick the robber nobles found a most implacable enemy.
Grattan from the first denounced the scheme with implacable hostility.
In the impeachment proceedings against Johnson, Sumner was one of the president's most implacable assailants.