This is the 1540th most frequent Portuguese word.
jamais
"Jamais" means "never" or "ever" (in a negative sense).
In this sentence, "jamais" is used to indicate an absolute negation, emphasizing that the speaker will never forget the mentioned day.
Eu jamais esquecerei aquele dia.
I will never forget that day.
Here, "jamais" conveys the idea of a strong denial or rejection of the possibility of repeating the mentioned action by the subject.
Ele prometeu que jamais faria isso novamente.
He promised that he would never do that again.
In this case, "jamais" expresses disbelief or surprise, showing that the speaker had no expectation or belief regarding the possibility of the stated event.