Showing no mercy or pity; harsh and cruel.
From Old French 'merci' combined with the English suffix '-less' (meaning 'without'). The word literally means 'without mercy' and emerged in Middle English as a way to describe particularly harsh behavior.
Ironically, the concept of 'mercilessness' is more a human invention than a natural trait—most animal behaviors we call 'merciless' are actually just instinctual survival, whereas humans are unique in choosing cruelty despite having the capacity for compassion.
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