astounding
dumbfounding
dumfounding
fabulous
implausible
improbable
marvellous
marvelous
tall
undreamed
undreamed of
undreamt
undreamt of
unimagined
a bit thick
a bit thin
absurd
antic
beyond belief
disbelievable
doubtable
doubtful
dubious
dubitable
fanciful
fantastic
flimsy
hard of belief
hard to believe
impossible
incomprehensible
inconceivable
incredible
mind-boggling
not deserving belief
open to doubt
open to suspicion
passing belief
preposterous
problematic
questionable
ridiculous
staggering belief
suspect
suspicious
thick
thin
unaccountable
unconvincing
unearthly
unexpected
ungodly
unimaginable
unsubstantial
unthinkable
unworthy of belief
weak
appal
astound
disconcert
horrify
indescribable
inexplicable
miraculous
scary
terrify
unbearable
unheard-of
unprecedented
achievable
believable
conceivable
receivable