In the Bible, sin is generally defined as any action, thought, or behavior that goes against God's commandments or moral laws. While murder is explicitly condemned as a grave sin in many parts of Scripture (such as in the Ten Commandments, Exodus 20:13), the concept of sin encompasses a broader range of actions and intentions.
The New Testament, particularly in the teachings of Jesus, expands the understanding of sin to include not only actions but also thoughts and intentions. For example, in Matthew 5:21-22, Jesus teaches that anger and insult towards another person can be considered as serious as the act of murder itself.
Therefore, while intentionally killing someone is certainly a sin, the Bible also addresses other forms of wrongdoing that may not involve such extreme actions but are still considered sinful. Overall, sin relates to the state of one's heart and relationship with God, not just specific actions.