1. occurring or done without being planned, forced, or prompted; natural and immediate
The audience gave a spontaneous round of applause.
O público deu uma salva de palmas espontânea.
2. acting or speaking without deliberation or premeditation; instinctive
She had a spontaneous reaction to the surprise party.
Ela teve uma reação espontânea à festa surpresa.
3. characterized by self-generated motion or activity; voluntary
The plant's spontaneous growth was remarkable.
O crescimento espontâneo da planta foi notável.