Is it ensure, insure, or assure?
c.1300, "Church father," from Old French doctour, from Medieval Latin doctor "religious teacher, adviser, scholar," in classical Latin "teacher," agent noun from docere "to show, teach, cause to know," originally "make to appear right," causative of decere "be seemly, fitting" (see decent). Meaning "holder of highest degree in university" is first found late 14c.; as is that of "medical professional" (replacing native leech (n.2)), though this was not common till late 16c. The transitional stage is exemplified in Chaucer's Doctor of phesike (Latin physica came to be used extensively in Medieval Latin for medicina).
Similar usage of the equivalent of doctor is colloquial in most European languages: cf. Italian dottore, French docteur, German doktor, Lithuanian daktaras, though these are typically not the main word in those languages for a medical healer. For similar evolution, cf. Sanskrit vaidya- "medical doctor," literally "one versed in science." German Arzt, Dutch arts are from Late Latin archiater, from Greek arkhiatros "chief healer," hence "court physician." French médecin is a back-formation from médicine, replacing Old French miege, from Latin medicus.
1590s, "to confer a degree on," from doctor (n.). Meaning "to treat medically" is from 1712; sense of "alter, disguise, falsify" is from 1774. Related: Doctored; doctoring.
doctor doc·tor (dŏk'tər)
A person, especially a physician, dentist, or veterinarian, trained in the healing arts and licensed to practice.
A person who has earned the highest academic degree awarded by a university in a specified discipline.
A person who drugs racehorses to improve their performance (1940s+ Horse racing)verb
(Luke 2:46; 5:17; Acts 5:34), a teacher. The Jewish doctors taught and disputed in synagogues, or wherever they could find an audience. Their disciples were allowed to propose to them questions. They assumed the office without any appointment to it. The doctors of the law were principally of the sect of the Pharisees. Schools were established after the destruction of Jerusalem at Babylon and Tiberias, in which academical degrees were conferred on those who passed a certain examination. Those of the school of Tiberias were called by the title "rabbi," and those of Babylon by that of "master."