a bit thick, a bit thin, absurd, beyond belief, debatable, doubtable, doubtful, dubious, dubitable, fishy, flimsy, hard of belief, hard to believe, hardly possible, improbable, inconceivable, incredible, more than doubtful, not deserving belief, open to doubt, open to suspicion, passing belief, preposterous, problematic, puzzling, questionable, ridiculous, staggering belief, suspect, suspicious, tall, thick, thin, unbelievable, unconvincing, unearthly, ungodly, unimaginable, unlikely, unpromising, unreasonable, unsubstantial, unthinkable, unworthy of belief, weak