From the outset, clearly this hierarchy of definitions will crescendo in the order cited. However, nowadays, these different terms are often confused or exchanged.
This term designates a person who lacks experience in practice in the exercise of a profession, an activity, a technique or an art.
This polysemic term sometimes common name and sometimes adjective qualifies in its first sense, a person who loves, cultivates, searches (certain things), like a music lover who can be a possible buyer.
An amateur is a person who engages in an activity outside his professional framework, generally without remuneration, and whose motivation comes essentially from passion. This activity can be artistic, sporting, etc.
It also designates a person who cultivates an activity, a technique, an art or a science for his sole pleasure and not by profession. An amateur talent.
In sport, this adjective qualifies the athlete, player or participant who practices without receiving direct remuneration as opposed to professional.
In the derogatory sense, it refers to a person who carries out an activity in a careless or fanciful manner. Amateur work.
The professional is a person exercising a profession or a trade.
Professionalism characterizes the quality and consistency of the work of an experienced person. Professionalism is the ability to ensure a commitment to society and to meet its expectations.
Consultant, Advisor or Counsel
Consultant is an anglicism, the translation of which is Counselor or Counselor, who designates a service provider in counseling who has proven expertise in a very specific field without being a specialist.
Advisers are often grouped together in consulting companies, or they act independently.
The consultant appoints a specialist outside an organization who is called upon to obtain advice on a question or to assist in solving a specific problem.
The specialist is the person with theoretical knowledge in one or more precise disciplines, frequently linked together, and is thus distinguished from the general practitioner with general knowledge.
The Expert is a person who, in addition to having theoretical knowledge in one or more areas of knowledge, has acquired in this or these same areas, advanced practical knowledge and recognized by his peers.
In addition, by his great experience, the expert is supposed to have acquired particular skills allowing him to carry out in particular expert opinions with the courts, governments, public communities and private institutions.