Synonyms and related words :
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