diligent
assiduous
cartilaginous
chewy
cohesive
constant
continuing
coriaceous
dedicated
determined
dogged
durable
enduring
faithful
fatigueless
fibrous
gristly
hard
hardy
immutable
inalterable
indefatigable
indomitable
industrious
inexhaustible
insistent
invincible
lasting
leatherlike
leathery
loyal
never-tiring
obstinate
patient
patient as Job
permanent
perseverant
persevering
persistent
persisting
pertinacious
plodding
plugging
preoccupied
rapt
relentless
resistant
resolute
ropy
ardent
self-denying
self-sacrificing
steadfast
strenuous
tireless
unceasing
unflagging
unsparing
unswerving
unwearied