Repetir vs. reiterar
While both repetir and reiterar translate to to repeat in English, they are not always interchangeable. Repetir is a very broad, common term, while reiterar is more formal and specific to restating something for emphasis or clarity.
Repetir
A1This is the most common and general-purpose word for to repeat. It can be used for almost any situation, including repeating actions, words, sounds, mistakes, a school year, or even a serving of food.
Pode repetir a última frase, por favor?
(Can you repeat the last sentence, please?)
Não quero repetir os mesmos erros do passado.
(I don't want to repeat the same mistakes from the past.)
Se não estudar, vai repetir o ano na escola.
(If you don't study, you will repeat the year at school.)
O jantar estava tão delicioso que eu pedi para repetir.
(The dinner was so delicious that I asked for a second helping.)
O alarme do carro não para de repetir o mesmo som.
(The car alarm won't stop repeating the same sound.)
A história tende a repetir-se.
(History tends to repeat itself.)
Reiterar
B2This is a more formal and specific verb. It means to repeat a statement, position, idea, or request, usually to add emphasis, reassert a point, or ensure there is no misunderstanding. It is almost exclusively used for verbal or written communication and is common in official, academic, legal, or business contexts.
Gostaria de reiterar o meu compromisso com a empresa.
(I would like to reiterate my commitment to the company.)
O ministro reiterou a importância do novo acordo comercial.
(The minister reiterated the importance of the new trade agreement.)
Para que não haja dúvidas, vou reiterar as instruções.
(So there are no doubts, I will reiterate the instructions.)
Na carta, o advogado reiterou o pedido de audiência.
(In the letter, the lawyer reiterated the request for a hearing.)
A cientista reiterou que os dados eram conclusivos.
(The scientist reasserted that the data was conclusive.)
Summary
In short, use repetir as the default, all-purpose verb for repeating anything, from actions to words. Use the more formal reiterar specifically when you mean to reaffirm or reassert a statement, idea, or position, typically in a formal setting to add emphasis or clarity. You would repetir a song, but reiterar a promise.