The Collaborative International Dictionary of English v.0.48:

Labile \La"bile\, a. [L. labilis apt to slip, fr. labi to slip.]
   1. Liable to slip, err, fall, or apostatize. [Obs.] --Cheyne.
      [1913 Webster]

   2. Liable or likely to change.
      [PJC]

   3. (Chem.) Easily decomposed or inactivated when subjected to
      heat, radiation, or mildly acidic or alkaline conditions;
      -- of chemical compounds; as, enzymes from thermophilic
      organisms are not as labile as those from mesophiles.
      [PJC]

WordNet (r) 3.0 (2006):

labile
    adj 1: (chemistry, physics, biology) readily undergoing change
           or breakdown
    2: liable to change; "an emotionally labile person"