The Collaborative International Dictionary of English v.0.48:

Acceptable \Ac*cept"a*ble\ (-s[e^]pt"[.a]*b'l; 277), a. [F.
   acceptable, L. acceptabilis, fr. acceptare.]
   Capable, worthy, or sure of being accepted or received with
   pleasure; pleasing to a receiver; gratifying; agreeable;
   welcome; as, an acceptable present, one acceptable to us.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acceptable
    adj 1: worthy of acceptance or satisfactory; "acceptable levels
           of radiation"; "performances varied from acceptable to
           excellent" [ant: unacceptable]
    2: judged to be in conformity with approved usage; "acceptable
       English usage"
    3: meeting requirements; "the step makes a satisfactory seat"
       [syn: satisfactory, acceptable]
    4: adequate for the purpose; "the water was acceptable for
       drinking"

Moby Thesaurus II by Grady Ward, 1.0:

73 Moby Thesaurus words for "acceptable":
   OK, adequate, admissible, adorable, agreeable, all right, alright,
   appetizing, attractive, average, bearable, better than nothing,
   commonplace, decent, delightful, desirable, eligible, endurable,
   enfranchised, enviable, exciting, fair, fairish, fit, fitted, good,
   good enough, goodish, grateful, gratifying, likable, lovable,
   moderate, mouth-watering, not amiss, not bad, not half bad,
   not so bad, okay, ordinary, passable, pleasant, pleasing,
   presentable, pretty good, provocative, qualified, respectable,
   satisfactory, satisfying, sufficient, suitable, supportable,
   taking, tantalizing, tempting, tenable, tidy, to be desired,
   tolerable, toothsome, unexceptionable, unexceptional,
   unimpeachable, unobjectionable, viable, welcome, winning,
   with voice, with vote, workmanlike, worth having, worthy