The phrase "cat o' nine tails" refers to a type of whip with nine lashes or thongs. Antonyms for this phrase could include peaceful, kind, gentle, and compassionate. These words represent a stark contrast to the violent and painful connotations associated with the cat o' nine tails. Other possible antonyms include loving, caring, nurturing, and empathetic. These words reflect a sense of humanity and understanding that is diametrically opposed to the cold, detached nature of using a whip to inflict harm. Overall, these antonyms remind us of the importance of treating others with kindness and respect, rather than resorting to violence and brutality.