1. (chemistry, physics, biology) readily undergoing change or breakdown;
2. liable to change; - Example: "an emotionally labile person"
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.
2. Liable or likely to change.
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.
WordNet (r) 3.0 (2006):
adj 1: (chemistry, physics, biology) readily undergoing change
2: liable to change; "an emotionally labile person"