The Collaborative International Dictionary of English v.0.48:

Fallible \Fal"li*ble\, a. [LL. fallibilis, fr. L. fallere to
   deceive: cf. F. faillible. See Fail.]
   Liable to fail, mistake, or err; liable to deceive or to be
   deceived; as, all men are fallible; our opinions and hopes
   are fallible.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fallible
    adj 1: likely to fail or make errors; "everyone is fallible to
           some degree" [ant: infallible]
    2: wanting in moral strength, courage, or will; having the
       attributes of man as opposed to e.g. divine beings; "I'm only
       a fallible human"; "frail humanity" [syn: fallible,
       frail, imperfect, weak]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "fallible":
   adulterated, blemished, careless, damaged, defective, deficient,
   errable, errant, erroneous, error-prone, faulty, found wanting,
   heedless, immature, impaired, imperfect, imprecise, impure,
   inaccurate, inadequate, incomplete, inexact, lacking,
   liable to error, makeshift, mediocre, mixed, not perfect, off,
   open to error, partial, patchy, short, sketchy, undeveloped,
   uneven, unfinished, unperfected, unsound, unthorough, wanting