This is the 425th most frequent Dutch word.
verleden
"Verleden" means "past" in English.
Here, 'verleden' is used as a noun meaning 'the past', referring to a past time period.
Ik heb een reis naar Rome gemaakt in het verleden.
I made a trip to Rome in the past.
In this sentence, 'verleden week' uses 'verleden' as an adjective meaning 'last' to indicate the previous week.
Hij heeft vergeten zijn werk verleden week af te maken.
He forgot to finish his work last week.
Here, 'verleden' is again a noun referring to 'the past', where it acts as the subject of reflection.