The Collaborative International Dictionary of English v.0.48:

Frankness \Frank"ness\, n.
   The quality of being frank; candor; openess; ingenuousness;
   fairness; liberality.
   [1913 Webster]

WordNet (r) 3.0 (2006):

frankness
    n 1: the quality of being honest and straightforward in attitude
         and speech [syn: candor, candour, candidness,
         frankness, directness, forthrightness]
    2: the trait of being blunt and outspoken [syn: frankness,
       outspokenness]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "frankness":
   accessibility, approachability, artlessness, austerity, baldness,
   bareness, big mouth, bluffness, bluntness, broadness, brusqueness,
   candidness, candor, coarseness, common speech, communicativeness,
   conversableness, directness, earthiness, effusion, effusiveness,
   extroversion, flow of words, flowing tongue, fluency,
   fluent tongue, flux de bouche, flux de paroles, flux of words,
   forthrightness, freedom, freeness, garrulity, garrulousness,
   gassiness, genuineness, gift of gab, glibness, gregariousness,
   grossness, gush, gushiness, homespun, household words,
   ingenuousness, leanness, long-windedness, loose tongue,
   loquaciousness, loquacity, matter-of-factness, naturalness,
   openheartedness, openness, outgoingness, outspokenness,
   plain English, plain dealing, plain speaking, plain speech,
   plain style, plain words, plainness, plainspokenness, prolixity,
   prosaicness, prosiness, raciness, rankness, rawness,
   restrainedness, roundness, rustic style, saltiness, severity,
   simpleness, simplicity, sincerity, slush, soberness, sociability,
   spareness, spate of words, spiciness, starkness,
   straightforwardness, talkativeness, unadorned style, unadornedness,
   unaffectedness, unconstraint, uncouthness, unimaginativeness,
   unpoeticalness, unrepression, unreserve, unreservedness,
   unrestraint, unrestriction, unreticence, unsecretiveness,
   unsuppression, untaciturnity, verbosity, vernacular, volubility,
   vulgarity, windiness