indelible

a. 不能消除的,不能拭除的,难忘的

His concern for the masses made an indelible impression on us.

他对群众的关怀给我们留下不可磨灭的印象。

Act promptly to remove spots from these fabrics. The longer you delay, the more indelible will the mark become.

赶快动手把这些污点从这些织物上擦掉。拖延时间越长，就越难擦掉。