1. (a.) That can not be removed, washed away, blotted out\, or effaced; incapable of being canceled, lost, or forgotten; as, indelible characters; an indelible stain; an indelible impression on the memory.

2. (a.) That can not be annulled; indestructible.

absorbing acute colorfast constant deathless deep deep-dyed deep-felt deepgoing double-dyed dyed-in-the-wool enduring fadeless fast fixed haunting heartfelt homefelt immortal imperishable impregnable incorruptible indestructible ineffaceable ineradicable inexpugnable inextinguishable ingrain ingrained invincible invulnerable keen lasting nagging nonperishable obsessive penetrating permanent persistent pervading piercing poignant profound quenchless recurrent sharp undampable undestroyable undying unerasable unfading unforgettable unquenchable