The Collaborative International Dictionary of English v.0.48:

Centennial \Cen*ten"ni*al\, n.
   The celebration of the hundredth anniversary of any event; a
   centenary. [U. S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Centennial \Cen*ten"ni*al\, a. [L. centum a hundred + annus
   year.]
   1. Relating to, or associated with, the commemoration of an
      event that happened a hundred years before; as, a
      centennial ode.
      [1913 Webster]

   2. Happening once in a hundred years; as, centennial jubilee;
      a centennial celebration.
      [1913 Webster]

   3. Lasting or aged a hundred years.
      [1913 Webster]

            That opened through long lines
            Of sacred ilex and centennial pines.  --Longfellow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

centennial
    adj 1: of or relating to or completing a period of 100 years;
           "centennial celebration" [syn: centennial, centenary]
    n 1: the 100th anniversary (or the celebration of it) [syn:
         centennial, centenary]