The Collaborative International Dictionary of English v.0.48:

Indefinitely \In*def"i*nite*ly\, adv.
   In an indefinite manner or degree; without any settled
   limitation; vaguely; not with certainty or exactness; as, to
   use a word indefinitely.
   [1913 Webster]

         If the world be indefinitely extended, that is, so far
         as no human intellect can fancy any bound of it. --Ray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

indefinitely
    adv 1: to an indefinite extent; for an indefinite time; "this
           could go on indefinitely"

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "indefinitely":
   a outrance, absolutely, all out, beyond all bounds, beyond compare,
   beyond comparison, beyond measure, broadly, completely, dead,
   downright, essentially, extremely, flat out, fundamentally,
   generally, immeasurably, in the extreme, incalculably,
   indecisively, indefinably, indeterminably, indistinctly,
   infinitely, most, obscurely, perfectly, purely, radically, totally,
   unconditionally, unequivocally, utterly, vaguely,
   with a vengeance