Humean, Humist, Pyrrhonic, Pyrrhonist, ambiguous, capricious, chancy, changeable, dicey, distrustful, doubter, doubtful, doubting, doubting Thomas, dubious, dubitante, equivocal, erratic, fickle, from Missouri, hesitant, hesitating, in doubt, incalculable, incredulous, indecisive, indemonstrable, irresolute, leery, mistrustful, mistrusting, polysemous, questioning, scoffer, scrupulous, shy, skeptic, skeptical, suspecting, suspicious, touch-and-go, unaccountable, uncertain, unconfirmable, unconvinced, undivinable, unforeseeable, unpersuaded, unpredictable, unprovable, unsure, untrusting, unverifiable, variable, wary, wavering, whimsical