practitioner (n.)

1540s, "one who acquires knowledge from actual practice;" a hybrid formed from practitian "practitioner" (c. 1500; see practician), with redundant ending on model of parishioner. Meaning "one engaged in the actual practice of an art or profession" is from 1550s. Johnson has as a secondary sense "One who uses any sly or dangerous arts" (compare practice (n.)). A general practitioner originally was "someone who practices both medicine and surgery."