Portuguese flag

Véspera de Ano-Novo vs. réveillon vs. passagem de ano

In Portuguese, véspera de Ano-Novo, réveillon, and passagem de ano all relate to New Year's Eve, but they emphasize different aspects of the event. While often interchangeable in casual conversation, distinct nuances exist regarding the calendar date, the specific celebration, and the moment of time transition.

Véspera de Ano-Novo

A2
This phrase literally translates to New Year's Eve. It refers specifically to the calendar day of December 31st, focusing on the period leading up to midnight rather than the party itself. It is the most descriptive and neutral way to refer to the date.
Muitas lojas fecham mais cedo na véspera de Ano-Novo.
(Many shops close earlier on New Year's Eve.)
Ela nasceu na véspera de Ano-Novo.
(She was born on New Year's Eve.)
Passamos a tarde da véspera de Ano-Novo cozinhando para o jantar.
(We spent the afternoon of New Year's Eve cooking for dinner.)
O trânsito fica terrível na véspera de Ano-Novo.
(Traffic gets terrible on New Year's Eve.)

Réveillon

B1
Borrowed from French, réveillon refers specifically to the celebration, the party, or the midnight supper. It is used extensively in Brazil to describe the festivities (fireworks, concerts, dinners). If you are talking about the event you are attending, this is the most common word.
Nós fomos convidados para um réveillon na praia.
(We were invited to a New Year's Eve party at the beach.)
O réveillon de Copacabana é famoso no mundo todo.
(The Copacabana New Year's celebration is famous worldwide.)
Eu preciso comprar uma roupa branca para o réveillon.
(I need to buy a white outfit for the New Year's party.)
O hotel oferece um pacote especial para o réveillon.
(The hotel offers a special package for the New Year's celebration.)

Passagem de ano

B1
This literally translates to the passage of the year. It refers to the transition moment or the act of crossing from one year to the next. While synonyms with the others, it is very commonly used in European Portuguese to mean New Year's Eve generally, whereas in Brazil it focuses on the turning point itself.
Vocês sabem onde vão passar a passagem de ano?
(Do you already know where you will spend the turn of the year?)
A passagem de ano foi marcada por muitos fogos de artifício.
(The turn of the year was marked by many fireworks.)
Eles preferem uma passagem de ano tranquila em casa.
(They prefer a quiet turn of the year at home.)
Desejamos a todos uma feliz passagem de ano.
(We wish everyone a happy New Year's transition.)

Summary

To summarize: use véspera de Ano-Novo when referring to the date of December 31st on the calendar. Use réveillon when talking about the party, the dinner, or the festive event itself. Use passagem de ano when referring to the moment of transition or the crossover into the new year.