[U] if someone shows mercy they choose to forgive or to be kind to someone who they have the power to hurt or punish

仁慈; 宽恕:

He showed no mercy to his enemies.

他对敌人毫不仁慈。

God have mercy on his soul.

愿上帝怜悯他的灵魂。

The boy was screaming and begging for mercy.

男孩尖叫着乞求宽恕。

at the mercy of sb / sth, unable to do anything to protect yourself from someone or something

任凭某人/某物的摆布〔而无力保护自己〕:

After the boat's motor failed, they were at the mercy of the weather.

船的马达坏了，他们只能听命于天气了。

She was completely at his mercy.

她完全听任他的摆布。

mercy flight / mission etc, a journey taken to bring help to people

救援飞行/任务等:

a mercy mission to help homeless refugees

帮助无家可归的难民的救援任务

leave sb to sb's (tender) mercies, to let someone be dealt with by another person, who may treat them very badly or strictly – used humorously

任凭某人受他人折磨（摆布）〔幽默用法〕

throw yourself on sb's mercy, to ask someone to help you or forgive you when you are in a very bad situation

乞求某人帮助（宽恕）自己

it's a mercy (that), [spoken] used to say that it is lucky that a worse situation was avoided

幸运的是（...），幸亏（...）:

It's a mercy the accident happened so near the hospital.

幸亏事故发生在离医院很近的地方。