Synonyms for Questionable:

adj.

at issue (adjective)
controversial.
disreputable (adjective)
dubious, infamous, contemptible, dishonorable, louche, risque, ribald, nefarious, disreputable, shifty, notorious, shady.
doubtful, uncertain (adjective)
arguable, indecisive, shady, hypothetical, paradoxical, unsettled, suspect, oracular, problematical, occult, dubitable, equivocal, disputable, mysterious, moot, iffy, apocryphal, debatable, vague, suspicious, cryptic, contingent, problematic, fishy, undefined, unreliable, dubious, provisional, controversial.
fallible (adjective)
in question.
shady (adjective)
shady.
uncertain (adjective)
contestable, mysterious, ambivalent, vague, debatable, deniable, insecure, changeable, precarious, undecided, confused, disputable, unsure, controversial, uncertain, arguable, moot, unconvinced, tentative.
unreliable (adjective)
undependable, untrustworthy, dubious, unreliable.

n.

fly-by-night, illegitimate, ill-favored, limited, dishonest, inferior, inadequate, poor, irregular, disagreeable, average, discreditable, unsatisfactory, undistinguished, substandard, honored, unsound, suboptimal, disappointing, unpopular. improbable, unlikely, Unapt, likely. honest. questionable (noun)
debatable, in question, problematical, dubious, so-called, deniable, suspicious, soi-disant, refutable, doubtful, self-styled, problematic, shady, apocryphal, supposed, suspect, funny, impugnable, alleged, dubitable, fishy, equivocal.

v.

supposed (verb)
hypothetical.

Other synonyms:

clouded, inexact, approximately, inaccurate, contested, unlikely, incorrect, roughly, Mootable, chancy, imprecise. improbable, unclear, inconclusive, dishonest, exceptionable, iffy. approximate, indecisive, wrong, broadly. Unapt. doubtful
doubtful.
marginal
borderline.
questionable
irregular.

Usage examples for questionable

  1. Yet it would even then remain questionable whether a good and great moral teacher is necessarily a good man. – The Faith of the Millions (2nd series) by George Tyrrell
  2. Whether she can find it there, may seem questionable – David Elginbrod by George MacDonald
  3. This constitutional position is so questionable that I strongly advise the members to resign promptly before the Lord Chamberlain gets them into trouble. – The Shewing-up of Blanco Posnet by George Bernard Shaw