This is the 5929th most frequent Korean word.
사서
"Librarian."
In this sentence, '사서' refers to a librarian, the professional person managing and organizing books in a library.
사서가 도서관에서 책을 정리하고 있어요.
The librarian is organizing books in the library.
Here, '사서' is used as a verb conjugated form of '사다' (to buy) combined with '-서', indicating the action of buying something.
나는 친구 생일 선물로 책을 사서 포장했어요.
I bought a book as a gift for my friend's birthday and wrapped it.
In this case, '사서' metaphorically means 'to incur' or 'bring upon oneself', denoting how one's actions can attract negative consequences.