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]

The Collaborative International Dictionary of English v.0.48:

Officiate \Of*fi"ci*ate\, v. t.
   To discharge, perform, or supply, as an official duty or
   function. [Obs.]
   [1913 Webster]

         Merely to officiate light
         Round this opacous earth.                --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

officiate
    v 1: act in an official capacity in a ceremony or religious
         ritual, such as a wedding; "Who officiated at your
         wedding?"
    2: perform duties attached to a particular office or place or
       function; "His wife officiated as his private secretary"
       [syn: officiate, function]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "officiate":
   act, act as, adjudicate, administer, administer the Eucharist,
   administrate, anoint, arbitrate, chair, chairman, chrism, conduct,
   confirm, direct, do duty, function, head up, hear, hold court,
   hold the scales, impose, judge, lay hands on, lead, manage,
   mediate, minister, moderate, occupy the chair, oversee,
   perform a rite, perform as, perform service, preside, preside over,
   referee, run, serve, sit in judgment, superintend, supervise, try,
   umpire