This is the 802nd most frequent Vietnamese word.
quen
"Quen" means "to forget" or "to be accustomed to," depending on context.
In this sentence, 'quen' is used to mean 'to be acquainted with' or 'to know someone'.
Tôi quen anh ấy từ lâu rồi.
I have known him for a long time.
Here, 'quen' means 'to get used to' or 'to adapt to' a certain situation or habit.
Bạn cần quen với cách làm việc mới.
You need to get accustomed to the new way of working.
In this context, 'quen' is part of the phrase 'đừng quen' to mean 'do not forget', where it indicates an unintentional forgetfulness.