The Collaborative International Dictionary of English v.0.48:

Officiate \Of*fi"ci*ate\, v. i. [imp. & p. p. Officiated; p.
   pr. & vb. n. Officiating.] [LL. officiare. See Office.]
   To act as an officer in performing a duty; to transact the
   business of an office or public trust; to conduct a public
   ceremony or service. --Bp. Stillingfleet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

officiating
    n 1: the act of umpiring; "the officiating was excellent" [syn:
         umpirage, officiation, officiating, refereeing]