The Collaborative International Dictionary of English v.0.48:

Centenary \Cen"te*na*ry\, n.; pl. Centenaries.
   1. The aggregate of a hundred single things; specifically, a
      century. "Every centenary of years." --Hakewill.
      [1913 Webster]

   2. A commemoration or celebration of an event which occurred
      a hundred years before.
      [1913 Webster]