The Collaborative International Dictionary of English v.0.48:

Participate \Par*tic"i*pate\, v. i. [imp. & p. p.
   Participated; p. pr. & vb. n. Participating.]
   To have a share in common with others; to take a part; to
   play a role; to partake; -- followed by in, formerly by of;
   as, to participate in a debate; to participate in a
   discussion. --Shak.
   [1913 Webster]

         So would he participate of their wants.  --Hayward.
   [1913 Webster]

         Mine may come when men
         With angels may participate.             --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

participating \participating\ adj.
   Taking part in an activity; as, the participating
   organizations.

   Syn: active.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

participating
    adj 1: taking part in an activity; "an active member of the
           club"; "he was politically active"; "the participating
           organizations" [syn: active, participating]