adjective
1.
not having or affording assurance of the certainty or soundness of something or someone
their chance of success is doubtful
Synonyms: ambiguous, borderline, clouded, doubtable, dubious, dubitable, equivocal, fishy, impugnable, indecisive, open, precarious, problematic, queasy, shady, shaky, suspect, suspicious, uncertain, unclear, undecided, uneasy, unsettled, unstable, unsure; compare moot
Related Word: question-begging; touch-and-go; chancy, insecure, questionable, speculative; hazy, obscure; unlikely; contingent, iffy
Idioms: at issue, in dispute, in doubt, in question
Contrasted words: decisive, open-and-shut, positive, sure; inarguable, incontestable, unarguable, undeniable, undoubted, unquestionable
Antonyms: indubitable
2.
Synonyms: moot , arguable, debatable, disputable, dubious, mootable, problematic, questionable, uncertain
3.
Synonyms: improbable 1, dubious, questionable, unlikely