to punish someone for something wrong that they did to you in the past and that you cannot forgive

Police believe the killer was a gang member settling a score with a rival gang. 警方认为，杀人犯是一团伙成员，当时正和敌对团伙算旧账。

He is using his wealth and power to settle old scores. 他凭借自己的财富和权力来算旧账。