A professional is a member of a profession or any person who earns their living from a specified professional activity. The term also describes the standards of education and training that prepare members of the profession with the particular knowledge and skills necessary to perform their specific role within that profession. In addition, most professionals are subject to strict codes of conduct, enshrining rigorous ethical and moral obligations. Professional standards of practice and ethics for a particular field are typically agreed upon and maintained through widely recognized professional associations, such as the IEEE. Some definitions of "professional" limit this term to those professions that serve some important aspect of public interest and the general good of society.
I pray thee cease thy counsel, Which falls into mine ears as profitless As water in a sieve.
William Shakespeare, Much Ado About Nothing (1598-99), Act V, scene 1, line 3. Reported in Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 10-11.