deathless
enduring
eternal
everlasting
extinguishable
immortal
imperishable
impregnable
incorruptible
indelible
indestructible
ineffaceable
ineradicable
inexpugnable
invincible
invulnerable
irrefragable
irrepressible
nonperishable
quenchless
undampable
undestroyable
undying
unquenchable
all-consuming
causeless
filial
inexpressible
pent-up
sincerest
unabated
unadulterated
unappeasable
unbounded
unbridled
unconquerable
undiluted
unextinguishable
unflagging
unreasoning
unrequited
white-hot