Definition
In a conclusive way that resolves an issue completely and permanently.
一勞永逸；徹底了結
We need to settle this dispute once and for all to prevent future issues.
我們需要一勞永逸地解決這場爭端，以防止未來的問題。
She decided to quit smoking once and for all.
她決定徹底戒菸。
The company pledged to handle all customer complaints once and for all.
公司承諾一勞永逸地處理所有客戶投訴。