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early 15c., "tutor, instructor" (earliest reference might be to "expert in the art of writing"), from Latin praeceptor "teacher, instructor," agent noun from praecipere (see precept). Medical training sense attested from 1803.
preceptor pre·cep·tor (prĭ-sěp'tər, prē'sěp'tər)
An expert or a specialist, such as a physician, who gives practical experience and training to a student, especially of medicine or nursing.