Source : Webster's Revised Unabridged Dictionary (1913)

Decennial \De*cen"ni*al\, a. [See {Decennary}.]
   Consisting of ten years; happening every ten years; as, a
   decennial period; decennial games. --Hallam.

Decennial \De*cen"ni*al\, n.
   A tenth year or tenth anniversary.