facultativo

adj. medical; facultative, optional; elective

n. practitioner; doctor, physician; lesson; faculty

adj. facultative, optional

= chief librarian.
Ex: The chief librarian or director of libraries, by which title the post is sometimes now known, will in general be fully occupied with making decisions on internal professional policy, committee work, and administration and management in the widest sense.
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* facultativos de bibliotecas = library faculty.