WordWeb Online

1. Lacking stability or fixity or firmness
   "unstable political conditions"; "the tower proved to be unstable in the high wind"; "an unstable world economy"
    
2. Highly or violently reactive
   "sensitive and highly unstable compounds"
    
3. Affording no ease or reassurance
   - precarious
    
4. Suffering from severe mental illness
   - mentally ill, unsound
    
5. Disposed to psychological variability
   "his rather unstable religious convictions"
    
6. Subject to change; variable
   "everything was unstable following the coup"
   - fluid

Derived forms: unstabler, unstablest

See also: changeable, changeful, coseismal, coseismic, crank, cranky, explosive, impermanent, inconstant, insane, irresolute, reactive, rickety, rocky, seismal, seismic, shaky, temporary, tender, tippy, tipsy, top-heavy, tottering, uneasy, unstableness, unsteady, volatile, volcanic, wobbly, wonky

Antonym: stable

Encyclopedia: Unstable