- the quality or state of being unstable; lack of stability or firmness.
- the tendency to behave in an unpredictable, changeable, or erratic manner: emotional instability.
noun plural -ties
- lack of stability or steadiness
- tendency to variable or unpredictable behaviour
- physics a fast growing disturbance or wave in a plasma
early 15c., from Middle French instabilite “inconstancy,” from Latin instabilitatem (nominative instabilitas) “unsteadiness,” from instabilis “unsteady,” from in- “not, opposite of” (see in- (1)) + stabilis (see stable (2)).