Same word, different country, different meaning
The grammar held together across the Atlantic remarkably well. The vocabulary did not, and a few of the divergences are the kind that stop a conversation rather than slow it down.
The first two below are worth knowing before you need them.
1. Propina
In Portugal, your propina is your tuition fee. It is on the university website, on the invoice, in the newspaper. Entirely neutral, entirely official.
In Brazil it means a bribe, in the criminal sense. So a Lisbon student mentioning to a Brazilian friend that they are off to pay their propina has said something quite different from what they meant, and the pause that follows is worth avoiding.
2. Rapariga
The ordinary Portuguese word for a girl or young woman. Used in newspapers, in novels, across the counter in a bakery, with nothing attached to it at all.
In Brazil the same word became an insult, with a strong implication of prostitution. This one runs in both directions: a Portuguese speaker can cause real offence in Brazil without any idea they have done it, and a Brazilian in Lisbon can be badly startled by how casually it gets used.
3. Apelido
In Portugal, your apelido is your surname. In Brazil it is your nickname, and the surname is your sobrenome.
This one has real consequences, because it is on every official form you will fill in. Asked for your apelido at the Finanças and answering with what your friends call you produces exactly the kind of afternoon you moved abroad to avoid. Sobrenome will be understood; apelido is what the form says.
4. Comboio, not trem
A train in Portugal is a comboio. The national operator is called Comboios de Portugal, so the word is unavoidable the moment you buy a ticket.