1. to complete a form, document, or space by writing all necessary information in detail
Please fill in the application form thoroughly before submitting it.
Por favor, preencha completamente o formulário de inscrição antes de enviá-lo.
2. to provide complete and detailed information about something
The detective asked the witness to fill in the details thoroughly about what happened.
O detetive pediu à testemunha que preenchesse completamente os detalhes sobre o que aconteceu.