critical
decisive
important
life-and-death
life-or-death
material
of import
pivotal
polar
aboriginal
acute
basal
basic
central
charged
clamorous
climacteric
compelling
cruciform
crying
deciding
desperate
dire
elemental
elementary
embryonic
emergent
essential
exigent
fundamental
generative
genetic
germinal
high-pressure
high-priority
imperative
imperious
in embryo
in ovo
insistent
instant
intersecting
kairotic
loaded
major
momentous
necessary
original
pregnant
pressing
primal
primary
primeval
primitive
relevant
specific
strategic
vital