When it comes to expressing an extreme lack of compassion or pity, the word "merciless" can feel quite strong. However, if you're looking to convey a similar sentiment with a slightly different nuance, there are plenty of synonyms to choose from. For example, "ruthless" emphasizes a willingness to act without hesitation or remorse. "Cruel" suggests a deliberate desire to inflict pain or suffering. "Heartless" implies a lack of empathy or emotional connection. "Inhumane" speaks to a disregard for basic human dignity. "Brutal" implies a harsh and violent approach. Ultimately, the right synonym will depend on the context and tone you're looking to convey.