Wiktionary:

arbiter | arbiters [plural] | arbitered [past tense] | arbitering [present participle]

Summary:

A person appointed, or chosen, by parties to determine a controversy between them; an arbitrator. | [With of] Any person who has the power of judging and determining, or ordaining, without control; one whose power of deciding and governing is not ...  (40 of 170 words, 3 senses, 1 etymology, pronunciation)

Link:

http://en.wiktionary.org/wiki/arbiter  [cite]

Encarta:

arbiter | arbiters [plural] | arbitral [adjective]

Summary:

somebody who can settle a dispute or decide an issue | somebody with great influence over what people say, think, or do  (21 of 48 words, 2 senses, 1 etymology, pronunciation)

Link:

http://encarta.msn.com/dictionary 1861586555/definition.html  [cite]