doubtable

adjective2

1. •
   Capable of being doubted; doubtful; dubious; dubitable. See usage notes below.

   • 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. — 1971
2. •
   (no longer used) Fearsome; redoubtable.