1. a person engaged in the practice of a profession, occupation, etc.:
a medical practitioner.
2. a person who practices something specified.
3. a person authorized to practice healing.
1. of or relating to a single or specific person, thing, group, class, occasion, etc., rather than to others or all; special rather than general
2. immediately present or under consideration; in this specific instance or place
3. distinguished or different from others or from the ordinary; noteworthy; marked; unusual
4. exceptional or especial
5. being such in an exceptional degree
6. dealing with or giving details, as an account or description, of a person; detailed; minute.
7. exceptionally selective, attentive, or exacting; fastidious; fussy
1. a person licensed to practice medicine, as a physician, surgeon, dentist, or veterinarian.
2. a person who has been awarded a doctor's degree
3. Doctor of the Church.
4. Older Slang. a cook, as at a camp or on a ship.
5. Machinery. any of various minor mechanical devices, especially one designed to remedy an undesirable characteristic of an automatic process.
6. Angling. any of several artificial flies, especially the silver doctor.
7. an eminent scholar and teacher.
Practitioner 從字典中查出有：實踐者,練習者;開業醫生。主要是指醫療方面的實踐、練習、開業 等等。
Specialist比較常用來指某個領域的專家。當然，當它指的是醫學方面的專家(specialist of medication)就是指醫生。
Doctor 感覺就是 普通醫生。
Practitioner 感覺像是 將怡學之適用於實踐的人。
Specialist 感覺偏向 高學歷、常常研究醫學方面知識的人。
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