noun
plural -cies
[noncount] :kind or forgiving treatment of someone who could be treated harshly
[noncount] :kindness or help given to people who are in a very bad or desperate situation
[count] :a good or lucky fact or situation
old-fashioned + informal - used as an interjection to show surprise
at the mercy of
or at someone's or something's mercy
in a position or situation in which you can be harmed by (someone or something you cannot control)
to the mercy of
or to the (tender) mercies of
without any protection from (someone or something you cannot control)