1. A psychological or psychiatric condition characterized by emotional volatility, unpredictable mood changes, and difficulty maintaining stable thoughts or behaviors
His mental instability made it difficult for him to maintain stable relationships.
A instabilidade mental dele tornava difícil manter relacionamentos estáveis.
2. A state of psychological imbalance or lack of emotional equilibrium
The trauma resulted in periods of mental instability.
O trauma resultou em períodos de instabilidade mental.
3. Legal or medical term referring to unsoundness of mind or psychiatric disorder
The court found evidence of mental instability in the defendant.
O tribunal encontrou evidência de instabilidade mental no réu.