metastable

1. Of uncertain stability; in a condition to pass into another phase when slightly disturbed; e.g., water, when cooled below the freezing point may remain liquid but will at once congeal if a piece of ice is added. 2. Denoting the excited condition of the nucleus of a radionuclide isomer that reaches a lower energy state by the process of isomeric transition decay without changing its atomic number or weight; e.g., Tc → Tc + γ. [meta- + L. stabilis, stable]

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meta·sta·ble .met-ə-'stā-bəl adj having or characterized by only a slight margin of stability <a \metastable compound>

meta·sta·bil·i·ty -stə-'bil-ət-ē n, pl -ties

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meta·sta·ble (metґə-sta″bəl) 1. a condition differing from stable in that, although the substance is stable in small perturbations, it can be transformed to a more stable condition by relatively large perturbations. 2. subject to inevitable change or destruction eventually, but apparently stable owing to slowness of change.