1. problematic; open to doubt or challenge.

- questionable motives

- a questionable reputation

- a fire of questionable origin

Similar word(s): contestable, alleged, supposed, apocryphal, debatable, problematic, problematical, doubtful, dubious, dubitable, equivocal, fishy, funny, shady, suspect, suspicious, impugnable

2. able to be refuted

Similar word(s): deniable, confutable, confutative, refutable

Sentences with questionable as an adjective:

- It is questionable if the universe is open or closed.

- Tiffiny's behavior is highly questionable.