unthinkable
a bit thick
a bit thin
absurd
antic
barred
beguiling
bewildering
beyond belief
closed-out
contrary to reason
doubtable
doubtful
dubious
dubitable
enigmatic
exceptional
excluded
extraordinary
fabulous
fanciful
fantastic
fascinating
hard of belief
hard to believe
hopeless
implausible
impossible
incomprehensible
inconceivable
incredible
logically impossible
marvelous
miraculous
not deserving belief
not possible
open to doubt
open to suspicion
outlandish
oxymoronic
paradoxical
passing belief
passing strange
phenomenal
preposterous
problematic
prodigious
prohibited
puzzling
unimaginability
astound
horrendous
immeasurable
incalculable
infinite
unbearable
unbelievable
unexplored
unfathomable
unheard-of
unimagined
unprecedented
unspeakable
imaginable
thinkable