arbiter elegantiarum
noun
arbiter el·e·gan·ti·a·rum -ˌe-lə-ˌgan-shē-ˈa-rəm 
-ˈer-əm
: a person who prescribes, rules on, or is a recognized authority on matters of social behavior and taste
Word History
Etymology
borrowed from Latin, literally, "arbiter of refinements"
First Known Use
1728, in the meaning defined above