noun.

Definitions: a person who has the power to settle an argument between people

Source: http://www.merriam-webster.com/dictionary/arbiter

I came across this word while reading “Texting Shorthand Annoys Purists and May Have Lasting Impact” by Seth Mydans. Page 1, paragraph #7

I now understand that the British Council has the power to settle arguments on the international use of English.