The Collaborative International Dictionary of English v.0.48:

Inversely \In*verse"ly\, adv.
   In an inverse order or manner; by inversion; -- opposed to
   directly.
   [1913 Webster]

   Inversely proportional. See Directly proportional, under
      Directly, and Inversion, 4.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inversely
    adv 1: in an inverse or contrary manner; "inversely related";
           "wavelength and frequency are, of course, related
           reciprocally"- F.A.Geldard [syn: inversely,
           reciprocally]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "inversely":
   a rebours, against the grain, arsy-varsy, backwards,
   bottom side up, bottom up, by contraries, contra, contrarily,
   contrariously, contrariwise, conversely, head over heels,
   heels over head, in flat opposition, just the opposite, nay rather,
   on the contrary, oppositely, otherwise, over, per contra,
   quite the contrary, rather, to the contrary, topsy-turvy,
   tout au contraire, turned around, upside down, vice versa