umpire

Concise Oxford English Dictionary © 2008 Oxford University Press:
umpire/ˈʌmpʌɪə(r)/

▶noun

• 1 (in certain sports) an official who watches a game or match closely to enforce the rules and arbitrate on matters arising from the play.

• 2 a person chosen to arbitrate between contending parties.

▶verb act as umpire in (a game or match).

– derivatives
umpirage noun,
umpireship noun.

– origin ME (orig. as noumpere): from OFr. nonper ‘not equal’; the n was lost by wrong division of a noumpere.