Mercy is used to describe a special journey to help someone in great need, such as people who are sick or made homeless by war.

If someone in authority shows mercy, they choose not to harm someone they have power over, or they forgive someone they have the right to punish.

If you refer to an event or a situation as a mercy, you mean that it makes you feel happy or relieved, usually because it stops something unpleasant from happening.

If one person or thing is at the mercy of another, the first person or thing is in a situation where they cannot prevent themselves from being harmed or affected by the second.