fearless
unafraid
assiduous
balanced
calm
constant
continuing
cool
coolheaded
diligent
dogged
enduring
faithful
fast
fiducial
firm
firm as Gibraltar
immutable
imperturbable
implacable
in equilibrium
inalterable
indefatigable
indomitable
industrious
inexcitable
insistent
invincible
lasting
loyal
merciless
mortal
nerveless
never-tiring
obstinate
patient
patient as Job
permanent
perseverant
persevering
persistent
persisting
pertinacious
plodding
plugging
predictable
preoccupied
rapt
relaxed
relentless
reliable
resolute
chivalrous
dauntless
intrepid
manly
self-sacrificing
single-minded
staunch
steadfast
strenuous
unalterable
unbending
unconquerable
unhesitating
unshaken
unshrinking
unsparing
unswerving
untiring
clinching
flinching
inching
lynching
pinching