1. to make a decision unintentionally or by chance, without deliberate intention
I decided accidentally to switch careers when I took that volunteer job.
Decidi acidentalmente mudar de carreira quando aceitei aquele trabalho voluntário.
2. to reach a conclusion or determination without planning to do so
We decided accidentally on that restaurant after getting lost.
Decidimos acidentalmente por aquele restaurante depois de nos perdermos.