[met-uh-stey-buh
l, met-uh-stey-] 
| 1. | Metallurgy. chemically unstable in the absence of certain conditions that would induce stability, but not liable to spontaneous transformation. |
| 2. | Also, labile. Physics, Chemistry. pertaining to a body or system existing at an energy level (metastable state) above that of a more stable state and requiring the addition of a small amount of energy to induce a transition to the more stable state. |
| met·a·sta·ble (mět'ə-stā'bəl) adj. Of, relating to, or being an unstable and transient but relatively long-lived state of a chemical or physical system, as of a supersaturated solution or an excited atom. met'a·sta·bil'i·ty (-stə-bĭl'ĭ-tē) n. |