The phrase "blow of mercy" is an idiomatic expression used to describe an act of kindness or compassion towards someone who is suffering or in distress. Synonyms for this phrase include "act of grace," "gesture of benevolence," "compassionate deed," and "merciful act." These terms convey a sense of empathy and understanding towards the recipient of the kindness. Other related phrases include "act of charity," "act of kindness," and "kindhearted deed." These expressions all describe acts of compassion and empathy towards others, emphasizing the importance of showing kindness and generosity towards those in need.