difficult to remove or forget
indelible - lasting
The word ‘indelible' is used to describe something long-lasting. That can be something that physically cannot be removed or erased, like a stain, or something that lives on long in the memory, whether for good or bad.
My mentor’s words left an indelible impression on me when I was just a young trainee. I remember them to this day.
A big part of the indelibility of the painter’s work is that it remains totally unique.
The events of that day are indelibly stamped on Mary’s mind. It was an horrific experience for her.