"pertaining or relating to the art or profession of healing or those who practice it," 1640s, from French médical, from Late Latin medicalis "of a physician," from Latin medicus "physician, surgeon, medical man" (n.); "healing, medicinal" (adj.), from medeor "to cure, heal," originally "know the best course for," from an early specialization of PIE root *med- "take appropriate measures" (source also of Avestan vi-mad- "physician"). "The meaning of medeor is based on a semantic shift from 'measure' to 'distribute a cure, heal'" [de Vaan]. The earlier adjective in English in this sense was medicinal. Related: Medically.
1917, short for medical examination. Earlier it was colloquial for "a student or practitioner of medicine" (1823).