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Use "mercilessness" in a sentence
"Reply Obj. 3: Cruelty is there taken for mercilessness, which is lack of beneficence."
"No humans perished in the blaze as the authorities stood idly by, but the firemen's mercilessness took on an added dimension when it was learned that the family's three dogs and cat died in the inferno."
"His ethics had been compressed into a fierce loyalty to friends and a mercilessness towards those who betrayed him."