Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. Happening once in a hundred years; as, centennial jubilee;
      a centennial celebration.

   3. Lasting or aged a hundred years.

            That opened through long lines Of sacred ilex and
            centennial pines.                     --Longfellow.

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

Source : WordNet®

centennial
     adj : of or relating to or completing a period of 100 years;
           "centennial celebration" [syn: {centenary}]

centennial
     n : the 100th anniversary (or the celebration of it) [syn: {centenary}]