A librarian was someone who worked in a library.
Edmund was a librarian for the Bodleian library in Oxford. (PROSE: Losing Track of Time)
Dr Armbruister was the senior librarian on the Braxiatel Collection. (PROSE: Sex Secrets of the Robot Replicants)
Yssaringintinka was an Ukkan librarian. (TV: Lost Library of Ukko)
The Eleventh Doctor frequently called Alice Obiefune "librarian", but she usually corrected him that she was a library assistant. (COMIC: After Life)