source: By Docteur Ando - Own work, CC BY-SA 4.0

a person actively engaged in an art, discipline, or profession, especially medicine:

(慣習などの)実践家; 実務家; 専門職従事者; 医者(medical practitioner)〘特に開業医; → general practitioner 〙; 弁護士

e.g. patients are treated by skilled practitioners.

mid 16th century: extension of obsolete practitian, variant of practician.