hard-hearted
heartless
unregenerate
unregenerated
adamant
asleep
benumbed
bony
brazen
callous
calloused
case-hardened
cement
cemental
cold
cold of heart
coldblooded
coldhearted
concrete
conscienceless
corneous
dead
deadened
dense
diamondlike
dogged
dour
dull
dure
firm
flinthearted
flintlike
flinty
fundamentalist
granitelike
granitic
hard
hard as nails
hard of heart
hard-bitten
hard-boiled
hard-nosed
hard-set
harden
hardened
hardhearted
harsh
hidebound
disobedient
fractious
immovable
imperious
implacable
indomitable
inexorable
inflexible
intractable
morose
mulish
obstinate
pertinacious
refractory
uncommunicative
unfeeling
unforgiving
ungovernable
unmanageable
unscrupulous