1. A sudden, natural urge or desire to act without premeditation or external influence
She acted on a spontaneous impulse to help the stranger.
Ela agiu por um impulso espontâneo de ajudar o estranho.
2. An unplanned, instinctive reaction or movement that occurs naturally
His spontaneous impulse was to run away from danger.
Seu impulso espontâneo foi fugir do perigo.