continual
implacable
adamant
adamantine
ardent
assiduous
bound
bound and determined
bowelless
cast-iron
ceaseless
certain
committed
constant
continuing
continuous
cruel
decided
decisive
dedicated
definite
determined
devoted
diligent
dog-eat-dog
dogged
dour
earnest
enduring
energetic
faithful
fated
fateful
ferocious
fervent
fierce
firm
flinty
fundamentalist
grim
habitual
hard
hard-core
hardworking
harsh
heartless
hidebound
immovable
immutable
impliable
frantic
incessant
inexorable
merciless
resolute
steady
unrelenting
compassionate
merciful