弄不掉、忘不掉
這一支就是畫面本身，而且一個字同時管兩邊：牆上的痕跡和心裡的記憶，狀態一樣。
adjective · C1
Impossible to rub out, wash off, or forget. An indelible mark stays on a surface however hard you clean it, and an indelible memory stays in your mind however much time passes.
擦不掉的；忘不了的
核心畫面
Picture ink dropped on white cloth. It does not sit on the surface; it works down into the threads. By the time you go back with water, it has become part of the cloth. Indelible names that state — someone tried to take it away and could not. The same picture carries a day you cannot stop remembering: it has soaked in.
可以想成墨水滴在白布上。它不是停在表面，是往纖維裡鑽。等你回頭拿水要洗的時候，它已經是布的一部分了。indelibl…更多收起
可以想成墨水滴在白布上。它不是停在表面，是往纖維裡鑽。等你回頭拿水要洗的時候，它已經是布的一部分了。indelible 講的就是這個狀態：有人想弄掉，弄不掉。這個畫面用在墨水上很直接。用在一段忘不了的往事上也一樣：那件事已經滲進去了。From the word’s history
From Latin indelebilis, meaning indestructible. Broken into parts it is in- (not) plus the root that also sits behind delete, so the word says, quite literally, cannot be deleted.
來自拉丁文 indēlēbilis，意思是「毀不掉的」。拆開看是 in-（不）加上跟 delete（刪除）同一條線的字根。可以想成這個字本身就寫著「刪不掉」。
Wiktionary etymology supplied in this evidence packet (source_ref kaikki:3f6f69a190036ae4:598557750): From Latin indelebilis (indestructible). By surface analysis, in- + delible.
Two branches
指明工具：寫下去就洗不掉
同一個畫面，只是把手指從痕跡移到工具上：不是說這道痕跡洗不掉，是說這支筆寫下去就洗不掉。
adjective · C1
Used in front of words like ink, pen, pencil, or marker to say that whatever you write with it cannot be washed off or rubbed out.
洗不掉的（墨水、筆）