(n.) One who doubts; one whose opinion is unsettled; one who scruples.

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