1.Definition: affording no ease or reassurance
2.Definition: disposed to psychological variability
"His rather unstable religious convictions"
3.Definition: highly or violently reactive
"Sensitive and highly unstable compounds"
4.Definition: lacking stability or fixity or firmness
"Unstable political conditions", "The tower proved to be unstable in the high wind", "An unstable world economy"
5.Definition: subject to change; variable
"Everything was unstable following the coup"
6.Definition: suffering from severe mental illness