This is the 17311th most frequent Polish word.
zamkn
The word "zamkn" alone is not complete in Polish; it is likely a truncated form of "zamknij," which means "close" (imperative form).
Here, 'zamknąć' is a verb in its infinitive form used in the polite imperative form, asking someone to close something.
Proszę zamknąć drzwi.
Please close the door.
In this sentence, 'zamknął' is a past tense form of the verb 'zamknąć', meaning 'he closed' to describe a completed action.
On zamknął książkę po przeczytaniu.
He closed the book after reading.
Here, 'zamknąć' is used in its infinitive form to describe the impossible action of closing, within the negative 'nie możesz' meaning 'you cannot'.