constant
resolute
abiding
accordant
adamant
age-long
aged
alike
ancient
antique
ardent
assiduous
automatic
balanced
calculable
changeless
chronic
committed
consistent
consonant
continuing
continuous
cool
correspondent
dedicated
deep-rooted
dependable
determined
devoted
diligent
diuturnal
dogged
durable
enduring
equable
equal
even
evergreen
faithful
faithworthy
fast
fiducial
firm
firm as Gibraltar
fixed
flat
flinty
frozen
candid
devout
immovable
indomitable
sincere
staunch
steady
uncompromising
unflinching
unselfish
unswerving
untiring
vigilant