critical
difficult
earnest
grave
hard
important
intellectual
of import
overserious
real
sedate
serious-minded
sincere
sober
sobering
solemn
solid
thoughtful
abandoned
acute
afire
alarming
ardent
arduous
austere
awe-inspiring
bad
bound
bound and determined
burning
businesslike
cogitative
cognitive
committed
comprehensive
concentrating
concentrative
conceptive
conceptual
conceptualized
consequential
considerable
contemplating
contemplative
crucial
dangerous
dangersome
decided
decisive
decorous
dedicated
deep
definite
deliberating
deliberative
demure
determined
devoted
devout
dignified
dour
elevated
excogitating
exhaustive
further
severe
significant
deleterious
delirious
imperious
mysterious
jesting
trifling
unimportant