bounden
compulsory
de rigueur
imposed
incumbent on
indispensable
mandatory
necessary
prerequisite
required
absolute
binding
choiceless
conclusive
decisive
decretory
demanded
dictated
entailed
essential
exigent
final
hard-and-fast
imperative
imperious
importunate
incumbent
inevitable
involuntary
irrevocable
mandated
must
necessitous
peremptory
prescript
prescriptive
requisite
ultimate
urgent
without appeal
without choice
obligate
obligated
obligation
obligational
obligato
obligatorily
oblige
obligee
obliger
obliging
obligingly
obligingness
obligor
acceptable
applicable
blameless
exhaustive
formal
fruitless
indefensible
informal
invariable
justifiable
legitimate
meaningless
meritorious
perfunctory
preliminary
unacceptable
unassailable
voluntary
optional