impossible to forget or remove 无法忘记的；不可磨灭的 (of ink, pens, etc. 墨水、钢笔等 leaving a mark that cannot be removed （笔迹）无法消除的，擦不掉的 an indelible marker 笔迹擦不掉的记号笔
Word Originlate 15th cent. (as indeleble): from French, or from Latin indelebilis, from in- ‘not’ + delebilis (from delere ‘remove, delete’). The ending was altered under the influence of -ible.