The Collaborative International Dictionary of English v.0.48:

Ostensibly \Os*ten"si*bly\ ([o^]s*t[e^]n"s[i^]*bl[y^]), adv.
   In an ostensible manner; avowedly; professedly; apparently.
   --Walsh.
   [1913 Webster]

         Ostensibly, we were intended to prevent filibustering
         into Texas, but really as a menace to Mexico. --U. S.
                                                  Grant.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ostensibly
    adv 1: from appearances alone; "irrigation often produces bumper
           crops from apparently desert land"; "the child is
           seemingly healthy but the doctor is concerned"; "had been
           ostensibly frank as to his purpose while really
           concealing it"-Thomas Hardy; "on the face of it the
           problem seems minor" [syn: apparently, seemingly,
           ostensibly, on the face of it]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "ostensibly":
   allegedly, apparently, arrantly, artificially, as a cover,
   as a pretext, as an excuse, as it seems, at first sight, avowedly,
   blatantly, boldly, clearly, conspicuously, demonstrably,
   erroneously, evidently, externally, factitiously, falsely,
   flagrantly, for public consumption, for the record, glaringly,
   in name only, manifestly, markedly, nominally, notably, noticeably,
   notoriously, obtrusively, obviously, on the surface, ostensively,
   outstandingly, outwardly, patently, plainly, plausibly,
   prima facie, professedly, prominently, pronouncedly, purportedly,
   saliently, seemingly, spuriously, staringly, strikingly,
   superficially, synthetically, to all appearances, to all seeming,
   to the eye, truthlessly, ungenuinely, unnaturally, untruly,
   unveraciously