Opponent : someone who competes with or opposes another in a contest, game, or argument. Specialist : a person who concentrates primarily on a particular subject or activity; a person highly skilled in a specific and restricted field. Amateur : a person who engages in a pursuit, especially a sport, on an unpaid rather than a professional basis. Expert : a person who is very knowledgeable about or skilful in a particular area. Dilettante : a person with an amateur interest in the arts.