The Collaborative International Dictionary of English v.0.48:

Foible \Foi"ble\, a. [OF. foible. See Feeble.]
   Weak; feeble. [Obs.] --Lord Herbert.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Foible \Foi"ble\, n.
   1. A moral weakness; a failing; a weak point; a frailty.
      [1913 Webster]

            A disposition radically noble and generous, clouded
            and overshadowed by superficial foibles. --De
                                                  Quincey.
      [1913 Webster]

   2. The half of a sword blade or foil blade nearest the point;
      -- opposed to forte. [Written also faible.]

   Syn: Fault; imperfection; failing; weakness; infirmity;
        frailty; defect. See Fault.
        [1913 Webster]

WordNet (r) 3.0 (2006):

foible
    n 1: a behavioral attribute that is distinctive and peculiar to
         an individual [syn: idiosyncrasy, foible, mannerism]
    2: the weaker part of a sword's blade from the forte to the tip

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "foible":
   bad habit, besetting sin, blemish, bug, catch, crack, crotchet,
   defect, defection, deficiency, drawback, eccentricity, failing,
   failure, fault, faute, flaw, frailty, hang-up, hole, idiosyncrasy,
   imperfection, inadequacy, infirmity, kink, little problem,
   moral flaw, peculiarity, preoccupation, problem, quirk, rift,
   shortcoming, snag, something missing, taint, vice,
   vulnerable place, weak link, weak point, weak side, weakness