1.Definition: affording no ease or reassurance

Related Adjective(s):precarious

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"

Related Adjective(s):fluid

6.Definition: suffering from severe mental illness

Related Adjective(s):unsound