merciful
adj.showing kindness and forgiveness to someone who could be punished. You use this to describe a person who has the power to be mean but chooses to be nice instead.
adj.showing or exercising compassion or forgiveness toward someone whom it is within one's power to punish or harm.
“The judge was merciful and gave the young man a light sentence.”
“After the long battle, the king proved to be a merciful leader by allowing the defeated soldiers to return home safely.”
“The sudden rain was a merciful relief to the farmers who had watched their crops wither under the relentless summer sun for weeks.”
Often used to describe people in positions of authority or events that end suffering.
From Middle English merciful, mercyful, equivalent to mercy + -ful. Displaced native Old English mildheort.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.