doubtable

doubt +‎ -able

doubtable (comparative more doubtable, superlative most doubtable)

1. (uncommon) Capable of being doubted; doubtful; dubious; dubitable. See usage notes below.
   • 1971, L. J. Swingle, "On Reading Romantic Poetry," PMLA, vol. 86, no. 5, p. 976,

     Descartes adopts the tool of a radical skepticism, submitting to question established beliefs, exposing them to the test of doubt, breaking them down when they prove doubtable.

2. (obsolete) Fearsome; redoubtable.

Philosophers often use "doubtable" in its literal sense of "capable of being doubted." In other scholarly and literary contexts, the more accepted direct synonym of "doubtable" is "dubitable." In all other usage, "doubtful" and "dubious" are far more common synonyms.

• (doubtful, dubious, capable of being doubted): uncertain

• undoubtable

• doubtable in An American Dictionary of the English Language, by Noah Webster, 1828.
• doubtable in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913.
• “doubtable” in Dictionary.com Unabridged, Dictionary.com, LLC, 1995–present.
• Oxford English Dictionary, 2nd ed., 1989.