Peace of mind

安心，心定（定心丸）, 放心無憂的狀態

例句:

房屋鑒定人徹底察看了房子以后，告訴我們可以放心買了。

The surveyor went over the house thoroughly and advised us that we can buy it with peace of mind.

誰也無法保證事情真相就能帶來快樂或是安心。

There is no guarantee that truth will bring happiness or peace of mind.

這不僅沒有讓她放心，反而帶來了更多的麻煩。

Far from giving her peace of mind , it had only created more trouble.

知道所有家人都在夜晚安然入睡真是讓人心定。

It is a peace of mind of going to sleep at night with everyone in the family safely in bed.

另外英語口語里面和peace相關的其它短語也有很多，比如：

At peace

不打仗，和平狀態

這兩個國家處于和平狀態。

The two countries were at peace.

In peace

1. 不打擾

你就不能讓我靜一會嗎？

Why can't you leave me in peace?

2. 不想打架

他們說他們來不是想打架的。

They said they came in peace.

Make peace

結束戰爭

兩個國家終于達成和解結束了戰爭。

The two countries finally made peace (with each other).