ar·bi·ter 
/ˈɑɚbətɚ/ noun
plural ar·bi·ters /ˈɑɚbətɚ/ noun [count] 1 : a person who is considered to be an authority on what is right, good, or proper — often + of ▪ an arbiter of fashion/manners/grammar ▪ He is regarded as an arbiter of taste in the world of jazz. 2 : a person who has the power to settle an argument between people
▪ The mayor will act as the final arbiter in any disputes between board members.
▪ The mayor will act as the final arbiter in any disputes between board members.
