undying (adj.)

• abiding
• amaranthine
• continuing
• continuous
• deathless
• everlasting
• frozen
• immortal
• imperishable
• impregnable
• incorruptible
• indefatigable
• indelible
• indestructible
• ineradicable
• inexpugnable
• inextinguishable
• interminable
• invincible
• invulnerable
• persistent
• quenchless
• remaining
• steady
• sticking
• sustained
• unceasing
• undestroyable
• unfading
• unquenchable
• unremitting