This is the 9998th most frequent Russian word.
арбитру
"Арбитру" means "to the referee" or "to the arbiter" (dative case of "арбитр").
The word 'арбитру' refers to the dative case of 'арбитор', meaning 'to the referee', and indicates the indirect object.
Арбитру было нелегко принять это решение.
It was difficult for the referee to make this decision.
Here, 'арбитру' is used in the dative case to indicate the recipient of the action (the referee).
Мяч был передан арбитру для проверки.
The ball was given to the referee for inspection.
The word 'арбитру' again appears in the dative case, denoting to whom the player is directing their request.