What does arbiter mean?
The definition of arbiter
Ar”bi*ter, n.
Etym: [L. arbiter; ar- (for ad) + the root of betere to go; hence properly, one who comes up to look on.]

1 A person appointed, or chosen, by parties to determine a controversy between them.

Note: In modern usage, arbitrator is the technical word.

2 Any person who has the power of judging and determining, or ordaining, without control; one whose power of deciding and governing is not limited. For Jove is arbiter of both to man. Cowper.

Synonyms
— Arbitrator; umpire; director; referee; controller; ruler; governor.

Ar”bi*ter, v. t.
To act as arbiter between. [Obs.]