The Collaborative International Dictionary of English v.0.48:

Honestly \Hon"est*ly\, adv.
   1. Honorably; becomingly; decently. [Obs.] --Chaucer.
      [1913 Webster]

   2. In an honest manner; as, a contract honestly made; to live
      honestly; to speak honestly. --Shak.
      [1913 Webster]

   To come honestly by.
      (a) To get honestly.
      (b) A circumlocution for to inherit; as, to come honestly
          by a feature, a mental trait, a peculiarity.
          [1913 Webster]

WordNet (r) 3.0 (2006):

honestly
    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]
    2: in an honest manner; "in he can't get it honestly, he is
       willing to steal it"; "was known for dealing aboveboard in
       everything" [syn: honestly, aboveboard] [ant:
       deceitfully, dishonestly, venally]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "honestly":
   authentically, blamelessly, bluntly, candidly, conscientiously,
   creditably, decently, dependably, disinterestedly, equitably,
   erectly, ethically, fairly, fastidiously, frankly, genuinely,
   high-mindedly, honorably, immaculately, impartially, in good faith,
   in plain English, in plain words, ingenuously, irreproachably,
   justly, legitimately, meticulously, morally, naturally, nobly,
   objectively, openly, plainly, punctiliously, purely, really,
   reliably, reputably, righteously, scrupulously, simply, sincerely,
   stainlessly, straightforwardly, truly, truthfully, unaffectedly,
   unambiguously, unassumedly, unequivocally, unimpeachably,
   unreservedly, unspottedly, uprightly, upstandingly, veridically,
   virtuously, warts and all, worthily