1. An aspiration or goal that seems unrealistic or unattainable; something desired that appears to have no chance of being achieved
Winning the lottery was his impossible dream.
Ganhar na loteria era seu sonho impossível.
2. An unrealistic or idealistic vision, often used to describe lofty ambitions that defy conventional wisdom
She chased her impossible dream of becoming an astronaut despite having no scientific background.
Ela perseguiu seu sonho impossível de se tornar uma astronauta apesar de não ter formação científica.