Pronunciation: (un-stā'bul),[key] —adj. 1. not stable; not firm or firmly fixed; unsteady.
2. liable to fall or sway.
3. unsteadfast; inconstant; wavering: unstable convictions. 4. marked by emotional instability: an unstable person. 5. irregular in movement: an unstable heartbeat. 6. Chem.noting compounds that readily decompose or change into other compounds.