Not stable; liable to change; insecure or unsteady in physical or mental condition.
経済が不安定だと企業の投資も慎重になる。
When the economy is unstable, companies become cautious about investment.
地面が不安定なので足元に気をつけてください。
The ground is unstable, so please watch your step.
彼の心は最近不安定で、よく気分が変わる。
His mind has been unstable lately and his mood changes often.