fortunate
unintended
accessory
accidental
additional
adscititious
adventitious
aleatory
appurtenant
ascititious
auxiliary
casual
causeless
chance
chancy
circumstantial
collateral
contingent
destinal
dicey
extra
fatal
fatidic
fluky
iffy
incidental
indeterminate
inessential
nonessential
odd
risky
secondary
subsidiary
superadded
superfluous
supervenient
supplemental
supplementary
uncaused
undetermined
unessential
unexpected
unforeseeable
unforeseen
unlooked-for
unpredictable
arbitrary
auspicious
coincidental
disastrous
favourable
illusory
improbable
inexplicable
opportune
providential
regrettable
transitory
unexplained
unimportant
unintentional
unrelated
unsatisfactory
untoward
circuitous