opinionist
/əˈpɪnjənɪst/noun
1A person who holds an opinion or doctrine against the generally accepted view; a dissenter. Now historical.
2The holder of any specified or implied opinion. In later use with prefixed adjective, as botanical, liberal, etc.
3A person whose business is to give a professional opinion; a person who decides a controversy.
Origin
Early 17th century; earliest use found in John Stephens (fl. 1611–1617), satirist and playwright. From opinion + -ist.