unconquerable
assiduous
beyond compare
beyond comparison
calculable
constant
continuing
deathless
dependable
diligent
dogged
easily first
enduring
facile princeps
faithful
faithworthy
fast
firm
immortal
immutable
impassable
impenetrable
imperishable
impregnable
inalterable
incomparable
incontestable
incorruptible
indefatigable
indelible
indestructible
indomitable
industrious
ineffaceable
ineradicable
inexpugnable
inextinguishable
inimitable
insistent
insuperable
insurmountable
inviolable
invulnerable
irresistible
lasting
loyal
matchless
never-tiring
nonperishable
nulli secundus
fierce
formidable
implacable
innate
instinctive
manly
resolute
stubborn
uncompromising
undying
victorious
conquerable
vincible