The Collaborative International Dictionary of English v.0.48:

hootenanny \hoot"en*an*ny\ n.
   1. An informal social gathering or concert featuring mostly
      folk songs, sometimes dancing, and where the audience
      often participates in the singing. [PJC]

   2. Same as whatchamacallit; a thingumbob. [Obsolescent,
      chiefly dial.]
      [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "hootenanny":
   affair, article, artifact, choral service, dingus, dofunny,
   dohickey, dojigger, dojiggy, domajig, domajigger, doodad, dowhacky,
   eisteddfod, eppes, etwas, farewell performance, flumadiddle,
   folk-music festival, folk-sing, gadget, gigamaree, gimmick, gizmo,
   hickey, hootmalalie, jam session, jigger, material thing,
   music festival, musicale, object, opera festival, quelque chose,
   rock festival, service of song, sing, sing-in, singfest, singing,
   something, swan song, thing, thingum, thingumabob, thingumadad,
   thingumadoodle, thingumajig, thingumajigger, thingumaree,
   thingummy, whatchy, widget