If you say that someone died peacefully, you mean that they suffered no pain or violence when they died.
例句
He died peacefully on 10th December after a short illness.病了一小段時間之后，他于12月10日安詳辭世。
英漢詞典釋義
adv.
平靜地;和平地
He lives straight and peacefully with his neighbours.他和他的鄰居坦誠而和睦地住在一起。Atheists and theists live together peacefully and amiably in this country.無神論者和有神論者在該國和睦相處。
英英詞典釋義
Adverb
1. in a peaceful manner;
"the hen settled herself on the nest most peacefully"