implausible
im-(in-) + plausible
adjective
(of an argument or statement) not seeming reasonable or probable; failing to convince:
信じがたい, ありそうもない
e.g. this is a blatantly implausible claim.
DERIVATIVES
implausibility |imˌplôzəˈbilədē| noun
implausibly |imˈplôzəblē| adverb