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):

tolerable
    adj 1: capable of being borne or endured; "the climate is at
           least tolerable" [ant: intolerable, unbearable,
           unendurable]
    2: about average; acceptable; "more than adequate as a
       secretary" [syn: adequate, passable, fair to middling,
       tolerable]