The Collaborative International Dictionary of English v.0.48:

Liable \Li"a*ble\ (l[imac]"[.a]*b'l), a. [From F. lier to bind,
   L. ligare. Cf. Ally, v. t., Ligature.]
   1. Bound or obliged in law or equity; responsible;
      answerable; as, the surety is liable for the debt of his
      principal.
      [1913 Webster]

   2. Exposed to a certain contingency or casualty, more or less
      probable; -- with to and an infinitive or noun; as, liable
      to slip; liable to accident.
      [1913 Webster]

   Syn: Accountable; responsible; answerable; bound; subject;
        obnoxious; exposed.

   Usage: Liable, Subject. Liable refers to a future
          possible or probable happening which may not actually
          occur; as, horses are liable to slip; even the
          sagacious are liable to make mistakes. Subject refers
          to any actual state or condition belonging to the
          nature or circumstances of the person or thing spoken
          of, or to that which often befalls one. One whose
          father was subject to attacks of the gout is himself
          liable to have that disease. Men are constantly
          subject to the law, but liable to suffer by its
          infraction.
          [1913 Webster]

                Proudly secure, yet liable to fall. --Milton.
          [1913 Webster]

                All human things are subject to decay. --Dryden.
          [1913 Webster]

WordNet (r) 3.0 (2006):

liable
    adj 1: at risk of or subject to experiencing something usually
           unpleasant; "he is apt to lose"; "she is liable to
           forget" [syn: apt(p), liable(p)]
    2: subject to legal action; "liable to criminal charges"
    3: (often followed by `to') likely to be affected with; "liable
       to diabetes" [syn: liable(p), nonimmune, nonresistant,
       unresistant]
    4: held legally responsible; "men between the ages of 18 and 35
       were liable for military service"

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "liable":
   accountable, actionable, amenable, answerable, answerable for, apt,
   assailable, attackable, beatable, blameworthy, bound, chargeable,
   conquerable, disposed, exposed, fair, foreseeable, given, hopeful,
   in the cards, inclined, likely, naked, nonimmune, obligated,
   obnoxious, odds-on, open, penetrable, pledged, predictable,
   predictable within limits, presumable, presumptive, probable,
   promising, prone, responsible, responsible for, sensitive,
   statistically probable, subject, susceptible, tied, to blame,
   verisimilar, vincible, vulnerable