The Collaborative International Dictionary of English v.0.48:

Participation \Par*tic`i*pa"tion\, n. [F. participation, L.
   participatio.]
   1. The act or state of participating, or sharing in common
      with others; as, a participation in joy or sorrows.
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            These deities are so by participation. --Bp.
                                                  Stillingfleet.
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            What an honor, that God should admit us into such a
            blessed participation of himself!     --Atterbury.
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   2. Distribution; division into shares. [Obs.] --Raleigh.
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   3. Community; fellowship; association. [Obs.] --Shak.
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WordNet (r) 3.0 (2006):

participation
    n 1: the act of sharing in the activities of a group; "the
         teacher tried to increase his students' engagement in class
         activities" [syn: engagement, participation,
         involvement, involution] [ant: non-engagement, non-
         involvement, nonparticipation]
    2: the condition of sharing in common with others (as fellows or
       partners etc.) [syn: participation, involvement]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "participation":
   admissibility, admission, affiliation, assimilation, association,
   companionship, company, completeness, comprehension,
   comprehensiveness, comprisal, consociation, cooperation, coverage,
   eligibility, embodiment, embracement, encompassment, envisagement,
   exhaustiveness, fellowship, fraternity, fraternization, inclusion,
   inclusiveness, incorporation, membership, openness, partaking,
   reception, sharing, society, tolerance, toleration, whole