To be undecided or skeptical about: began to doubt some accepted doctrines. To tend to disbelieve; distrust: doubts politicians when they make sweeping statements. To regard as unlikely: I doubt that we'll arrive on time. Archaic To suspect; fear. To be undecided or skeptical. A lack of certainty that often leads to irresolution. See Synonyms at uncertainty. A lack of trust. A point about which one is uncertain or skeptical: reassured me by answering my doubts. The condition of being unsettled or unresolved: an outcome still in doubt. beyond Without question; certainly; definitely. no doubt Certainly. no doubt Probably.