The Collaborative International Dictionary of English v.0.48:

Tolerable \Tol"er*a*ble\, a. [L. tolerabilis: cf. F.
   tol['e]rable. See Tolerate.]
   1. Capable of being borne or endured; supportable, either
      physically or mentally.
      [1913 Webster]

            As may affect the earth with cold and heat
            Scarce tolerable.                     --Milton.
      [1913 Webster]

   2. Moderately good or agreeable; not contemptible; not very
      excellent or pleasing, but such as can be borne or
      received without disgust, resentment, or opposition;
      passable; as, a tolerable administration; a tolerable
      entertainment; a tolerable translation. --Dryden.
      [1913 Webster] -- Tol"er*a*ble*ness, n. --
      Tol"er*a*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tolerably
    adv 1: in an acceptable (but not outstanding) manner; "she plays
           tennis tolerably" [syn: acceptably, tolerably, so-
           so] [ant: intolerably, unacceptably]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "tolerably":
   acceptably, adequately, admissibly, after a fashion, agreeably,
   amply, appreciably, at any rate, at best, at least, at most,
   at the least, at the most, at the outside, at worst,
   commensurately, comparatively, decently, detectably, enough,
   fair to middling, fairishly, fairly, fairly well, in a manner,
   in a way, in part, in some measure, incompletely, indifferently,
   leastwise, mediocrely, merely, middling well, middlingly, mildly,
   moderately, modestly, not comprehensively, not exhaustively, only,
   part, partially, partly, passably, presentably, pretty,
   pretty well, pro tanto, purely, rather, relatively, respectably,
   satisfactorily, satisfyingly, simply, so far, so-so, somewhat,
   sufficiently, thus far, to a degree, to some degree,
   unexceptionably, visibly, well enough