a professional person trained in library science and engaged in library services
"The new librarian spent her first week organizing books by subject to improve access for patrons."
The keeper, manager of a library.
"The librarian carefully organized the new books on the shelves."
In plain English: A librarian is someone who works at a library to help people find books and manage collections.
"The librarian helped me find a book for my history project."
Librarian is a compound word formed from library and the suffix -an. It first appeared in English around 1710 to describe someone who manages or works in a library.