nihilism

unbelief, disbelief, misbelief; discredit, miscreance; infidelity (irreligion); dissent; change of opinion; retractation., doubt (uncertainty); skepticism, misgiving, demure; distrust, mistrust; misdoubt, suspicion, jealousy, scruple, qualm; onus probandi., incredibility, incredibleness; incredulity., unbeliever.

disbelieve, discredit; not believe; misbelieve; refuse to admit (dissent); refuse to believe (incredulity)., doubt; be doubtful (uncertain); doubt the truth of; be skeptical as to; diffide; distrust, mistrust; suspect, smoke, scent, smell a rat; have doubts, harbor doubts, entertain doubts, suspicions; have one's doubts., demure, stick at, pause, hesitate, scruple; stop to consider, waver., hang in suspense, hang in doubt., throw doubt upon, raise a question; bring in, call in question; question, challenge, dispute; deny; cavil; cause a doubt, raise a doubt, start a doubt, suggest a doubt, awake a doubt, make suspicion; ergotize, startle, stagger; shake one's faith, shake one's belief, stagger one's faith, stagger one's belief.

unbelieving; incredulous as to, skeptical as to; distrustful as to, shy as to, suspicious of; doubting, doubtful (uncertain); disputable; unworthy of, undeserving of belief [more]; questionable; suspect, suspicious; open to suspicion, open to doubt; staggering, hard to believe, incredible, not to be believed, inconceivable., fallible (uncertain); undemonstrable; controvertible (untrue).

cum grano salis [Latin: with a grain of salt]; with grains of allowance.