indelible (adj.)

• absorbing
• acute
• colorfast
• constant
• deathless
• deep
• double-dyed
• enduring
• fast
• fixed
• haunting
• heartfelt
• immortal
• imperishable
• impregnable
• incorruptible
• indestructible
• ineradicable
• inexpugnable
• inextinguishable
• ingrained
• invincible
• invulnerable
• keen
• lasting
• nagging
• obsessive
• penetrating
• permanent
• persistent
• piercing
• poignant
• profound
• quenchless
• recurrent
• sharp
• undestroyable
• undying
• unerasable
• unfading
• unforgettable
• unquenchable