1. 
   Octennial
   Oc·ten'ni·al adjective [ Latin octennium a period of eight years; octo eight + annus year.] Happening every eighth year; also, lasting a period of eight years. Johnson. -- Oc*ten'ni*al*ly , adv...
   Found op http://www.encyclo.co.uk/webster/O/9
   
   
2. 
   Octennial
   • (a.) Happening every eighth year; also, lasting a period of eight years.
   Found op http://thinkexist.com/dictionary/meaning/octennial/
   
   
3. 
   octennial
   1) Happening every eight years 2) Occurring every other leap year, say
   Found op http://www.mijnwoordenboek.nl/EN/crossword-dictionary/octennial/1
   
   

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