Humism, Pyrrhonism, agnosticism, agonize over, all-overs, anxiety, apprehension, apprehensiveness, awake a doubt, be at sea, be diffident, be doubtful, be dubious, be possessive, be skeptical, be uncertain, beat about, call in question, challenge, concern, confutability, contest, contestability, controvertibility, deniability, diffidence, disbelief, disbelieve, discredit, disputability, dispute, disquiet, distrust, distrustfulness, doubtful, doubtfulness, dubiety, dubiousness, dubitancy, fear, feel unsure, flounder, fluctuate, foreboding, greet with skepticism, grope, half-belief, half believe, harbor suspicions, have reservations, hesitate, hesitation, in doubt, incertitude, incredulity, irresolution, leeriness, misdoubt, misgive, misgiving, mistrust, mistrustfulness, puzzle over, qualm, qualmishness, query, question, questionableness, raise a question, refutability, reservations, scepticism, scoff, scoffing, scruple, scrupulousness, self-doubt, shadow of doubt, skepticalness, skepticism, smell a rat, suspect, suspicion, suspiciousness, thrash about, throw doubt upon, total skepticism, treat with reserve, unbelief, uncertainty, vacillate, wariness, waver, wonder, wonder whether, worry