to blot out or erase completely at one stroke, typically referring to achievements, history, or merits

尽管他现在犯了错，但我们不能将他以往的功劳一笔抹杀。

to dismiss out of hand or deny something without a fair hearing or consideration

你不能对他提出的方案一笔抹杀，至少应该先听听他的理由。