Englishunconvincing
adjective
he had a plausible though highly unconvincing story:
improbable, unlikely, implausible;
incredible, scarcely credible, unbelievable, difficult to believe, beyond belief, questionable, dubious, doubtful;
strained, labored, ponderous, forced, far-fetched, remote, unrealistic, fanciful, fantastic, strange;
feeble, weak, unsound, thin, transparent, poor, lame, trifling, shallow, inadequate, unsatisfactory, ineffectual, half-baked, pathetic;
informal hard to swallow/take.
▷antonyms convincing, cogent, persuasive.