The Collaborative International Dictionary of English v.0.48:

Frankly \Frank"ly\, adv.
   In a frank manner; freely.
   [1913 Webster]

         Very frankly he confessed his treasons.  --Shak.

   Syn: Openly; ingenuously; plainly; unreservedly;
        undisguisedly; sincerely; candidly; artlessly; freely;
        readily; unhesitatingly; liberally; willingly.
        [1913 Webster]

WordNet (r) 3.0 (2006):

frankly
    adv 1: (used as intensives reflecting the speaker's attitude) it
           is sincerely the case that; "honestly, I don't believe
           it"; "candidly, I think she doesn't have a conscience";
           "frankly, my dear, I don't give a damn" [syn: honestly,
           candidly, frankly]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "frankly":
   all joking aside, bluffly, bluntly, broadly, brusquely, candidly,
   directly, genuinely, in all conscience, in all seriousness,
   in plain English, in plain words, openheartedly, openly,
   outspokenly, plain-spokenly, plainly, roundly, sincerely,
   straightforwardly, unconstrainedly, unreservedly, unrestrainedly,
   with no nonsense