na-adjective
Describes a process or resolution that is carried out peacefully, without conflict. Typically used in the adverbial form 平和裏に, often in formal or written contexts.
交渉は平和裏に進められた。
The negotiations were conducted peacefully.
問題が平和裏に解決されることを望む。
I hope the issue will be resolved amicably.
Compound of 平和 (peace) and 裏 (back, inside), here used in the sense of 'in a state of'. The exact derivation is uncertain; the word is relatively uncommon and formal.