doubtful

[dout-fuhl]
adjective
  1. of uncertain outcome or result.
  2. admitting of or causing doubt; uncertain; ambiguous.
  3. unsettled in opinion or belief; undecided; hesitating.
  4. of equivocal or questionable character: His tactics are highly doubtful.

Origin of doubtful

First recorded in 1350–1400, doubtful is from the Middle English word douteful. See doubt, -ful
Related formsdoubt·ful·ly, adverbdoubt·ful·ness, nounpre·doubt·ful, adjectivepre·doubt·ful·ly, adverbqua·si-doubt·ful, adjectivequa·si-doubt·ful·ly, adverbun·doubt·ful, adjectiveun·doubt·ful·ly, adverbun·doubt·ful·ness, noun

Synonyms for doubtful

Synonym study

3. Doubtful, dubious, incredulous, skeptical imply reluctance or unwillingness to be convinced. To be doubtful about something is to feel that it is open to question or that more evidence is needed to prove it: to be doubtful about the statements of witnesses. Dubious implies vacillation, unsureness, or suspicion: dubious about suggested methods of manufacture. Incredulous means unwilling or reluctant to believe: incredulous at the good news. Skeptical implies a general disposition to doubt or question: skeptical of human progress.

Antonyms for doubtful

1, 2. certain.

Usage note

See doubt.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for undoubtfully

doubtful

adjective
  1. unlikely; improbable
  2. characterized by or causing doubt; uncertaina doubtful answer
  3. unsettled; unresolved
  4. of questionable reputation or morality
  5. having reservations or misgivings
  6. (of a sportsperson) not likely to be fit enough to play or take part
noun
  1. a person who is undecided or uncertain about an issue
  2. a sportsperson who is not likely to be fit enough to play or take part
Derived Formsdoubtfully, adverbdoubtfulness, noun

usage

It was formerly considered correct to use whether after doubtful (it is doubtful whether he will come), but now if and that are also acceptable
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for undoubtfully

doubtful

adj.

late 14c., from doubt (n.) + -ful. Related: Doubtfully; doubtfulness.

Online Etymology Dictionary, © 2010 Douglas Harper