metastable Syllabification: (met·a·sta·ble)Pronunciation: /ˈmetəˌstābəl, ˌmetəˈstābəl/Definition of metastable adjective Physics (of a state of equilibrium) stable provided it is subjected to no more than small disturbances. (of a substance or particle) theoretically unstable but so long-lived as to be stable for practical purposes. Derivatives metastabilityPronunciation: /-stəˈbilətē/ noun metastable in other Oxford dictionaries Definition of metastable in the British & World English dictionary