If you say that someone is implacable, you mean that they have very strong feelings of hostility or disapproval which nobody can change.
例句
...the threat of invasion by a ruthless and implacable enemy...残暴无情的敌人发出的侵略威胁The move has won the implacable opposition of many economists.该提案遭到了许多经济学家的坚决反对。