Professional

A professional is someone who has a specialised job which only very well trained people can perform, such as  Doctors, lawyers, and teachers. These occupations are known as professional occupations. They may often get paid more than other people. In sport, a professional is someone who is paid to play. For example, Petra Kvitová and Tim Cahil are professional sportspeople.

The word "professional" is often used as an adjective, e.g.
 "He did a thoroughly professional job" (meaning: a very good one, even if he was not a professional).
 "His behaviour was always professional" (meaning: he behaved in a proper way, like someone of his profession should).
The opposite of "professional" in this sense is: "unprofessional".

Another word that is the opposite of "professional" is "amateur". This means that someone does not get paid for the job he is doing (even if he may be doing it very well).

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